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The Black Raven Conspiracy

Chapter Text

It was the second week in April, and springtime was coming to Hogwarts Castle. Though about half of the days remained somewhat glum and rainy, signs of new life were popping up all over the grounds. In the greenhouses, Professor Sprout's honking daffodils were blossoming, and the peas in the groundskeeper Hagrid's garden were lit up with spots of brilliant pink. Up on the mountains and at the edges of the Forbidden Forest, marsh violet and wild gorse stained the ground purple and sunshine yellow. Even the violent Whomping Willow looked beautiful, with fluffy flowers that it shook at passing students, creating a light dusting of gold on their black robes.

But inside the castle, one particular student was not feeling the joys of spring. Sherlock Holmes was in his third year at Hogwarts, and it had proven to be an interesting year in and of itself. Third year was when students were allowed to choose their elective courses. He'd thoroughly enjoyed all three of his new courses: Care of Magical Creatures, the rare offering Ghoul Studies, and most of all Arithmancy, the magic of numbers. Professor James, the Arithmancy teacher, particularly intrigued him, with his oddly vacant dark eyes and soft Irish accent.

Nonetheless, third year had proven a little on the frustrating side. Sherlock's best friend John Watson had had great success with the story of last year's case, "The Hound of Hogwarts." All this year Sherlock had gotten requests from students to solve their problems. To his own surprise, he'd actually taken on a few, mainly at promptings from John and his other friend Molly Hooper. None of them had been, in his opinion, cases worthy of remembering. But John, in response to demand from Professor Binns (who ran the Hogwarts newsletter), wrote up several of these smaller cases. So on top of not having interesting puzzles to solve, Sherlock was having to cope with his newfound fame and subsequent lack of privacy.

His morning walk to the Great Hall for breakfast told Sherlock that it was going to be one of those days. The Slytherin common room was deserted, and he was loath to leave the comfort of its soft emerald light and lapping lake water. But he had to eat, so he took a deep breath and exited through the concealed stone door. Up through the snaking corridors, all the way to the Hall, Sherlock felt the burning of eyes on the back of his neck, heard students whispering his name behind their hands. Just outside the hall, a small knot of Gryffindors and one Ravenclaw seemed to be waiting for him.

"Morning, Holmes." The sneering voice of Sally Donovan greeted Sherlock, and he held back a sigh. Donovan nodded her brown curls at another of the Gryffindors. "Joey here wants to know if you can find his missing trousers." Sherlock felt his face burn as the group laughed, drawing more stares from passing students. He shoved past them, giving the lanky Ravenclaw Phil Anderson a particularly cold stare. To his relief, Molly was walking towards him from the Hufflepuff table.

"Oh, good, you're here," she said, smiling at him. "John and I waited for you. Want to take some breakfast outside?"

"Oh, God, yes."

Shortly afterward, the three friends were carrying plates from the Great Hall onto the blooming grounds. It was a habit they'd gotten into last year. It was much easier, and far more pleasant, to come out here and share a meal while discussing cases. But the habit had extended well beyond case times, because it offered a bit of peace to three people widely regarded as misfits. No one in the castle could berate them for their unusual friendship group - a Gryffindor, a Slytherin, and a Hufflepuff - out here. They sat underneath their favorite tree on the banks of the Black Lake. John passed around slices of buttered toast with jam and marmalade, Sherlock handed out thick bacon slices, and the three of them tucked in.

"Guess what," Molly said after a moment.

"What?" John and Sherlock said together.

Molly took a deep breath. A blush was coming into her face, but it was an excited one. "Remember how Professor Sprout took me aside after Herbology yesterday?" The boys nodded, and Molly charged on, her brown eyes sparkling. "She asked me to be a Herbology tutor. Six Galleons an hour, ten hours over each week."

"That's brilliant!" exclaimed John. He threw one arm around Molly's shoulders.

"Congratulations," said Sherlock. Though he was not as good at expressing affection as John, he gave Molly his biggest smile. She deserved their praise: usually Hogwarts tutors were only appointed after they'd taken their O.W.L.s. More proof, as if Sherlock and John needed it, that their friend had a good brain in her head.

"Thank you," she said, beaming. "I'll be working with the first- and second-years, and add new years as we move up." Her smile faded a little as she looked at Sherlock. "I just hope it won't...you know. Interfere with cases."

Sherlock pushed aside the slight, uncomfortable quiver he got whenever Molly voiced his own thoughts. "It shouldn't," he said, "if only we can land an actual case instead of the tiny things John's been writing up."

"Hey, now, those 'tiny things' are earning me three Galleons a pop," John said, but he looked sympathetic. Glancing around, he asked through a mouthful of bacon, "You really haven't had anything?"

"Not recently." Seeing a little smirk on Molly's face, Sherlock said, "What have you been up to?"

"Oh, nothing," she said cheerily. "It's just that Soo Lin asked if she could talk to you later today." Soo Lin Yao, a friend of Molly's who was in Ravenclaw, had proved to be a vital connection to Ravenclaw House in their previous two major investigations. "She seemed pretty worried, and said she wanted to talk only to you. Sounds promising, don't you think?"

It did sound promising, and as they finished their breakfast Sherlock felt his mood lift slightly. Maybe this wouldn't turn out to be one of those days after all.

Chapter Text

Sherlock waited impatiently for evening to come, so that he could speak to Soo Lin Yao. As promised, Molly had her meet Sherlock in the Entrance Hall immediately after dinner. The girl's straight, dark hair was pulled back in a long plait, and her slightly round face was more serious than usual. She held a small bunch of paper in her right hand, and the left hand's fingers picked nervously at each other. Whatever this was about, it was obviously causing her some worry.

"Hi, Soo Lin," said Sherlock. She didn't answer, but acknowledged his greeting with a small, tight smile.

"Shall we go, then?" Sherlock said. He turned towards the tapestry concealing the flight of stairs to the dungeons. As he pushed the green, silver-bordered forest scene aside Soo Lin glanced at him.

"Aren't we going to talk about my case?" she said tensely.

"Of course," Sherlock said. He led the way down into the torchlit dungeon corridors, turning away from the hall that led towards the Potions classroom. He saw Soo Lin shiver slightly in the drafty stone halls. "We're going to the Slytherin common room. Don't worry," he added lazily as she opened her mouth, "none of the Slytherins bother with me."

"Why - "

"Molly and John," he said shortly.

"Oh." Soo Lin nodded, and Sherlock knew he didn't need to say any more. They stopped outside the bare stretch of stone wall hiding the Slytherin common room's entrance. It was virtually indistinguishable from the rest of the wall but for one thing: a tiny snake etched into the stone, in the center of the door.

"Bat's wool," Sherlock said, and the stone door slid smoothly aside to admit them. A few of his fellow Slytherins were lounging about in the black leather chairs. But the instant they saw the Ravenclaw with Sherlock, they melted away into dormitories. The two third-years sat at an ornately carved table near the roaring fire, Soo Lin wrapping her arms around herself.

"So, what seems to be your trouble?" Sherlock asked.

Soo Lin took a deep breath. As she started to speak, Sherlock saw her fingering the pieces of parchment in her hand. "Thank you for meeting me alone. Normally I'd be fine with Molly and your friend Watson being here, but..."

"Sometimes you need an objective party," Sherlock said.

Soo Lin nodded and continued. "How much do you know about Ancient Runes?"

"Not much. It's Molly who's taking the class."

"Oh!" Soo Lin's eyes widened a bit. "Well, then, you can bring these to her and ask what she makes of them." She took the pieces of parchment and spread them across the table. Bending over them, Sherlock saw a series of odd, spiked shapes scrawled on the parchment. At the bottom of each sheet, in Soo Lin's neat hand, was a date and a location in the castle.

"They've been showing up all over Hogwarts," she said. Pointing, she added, "This was the first one, scratched into a wall outside the Ravenclaw common room."

"Next, three days later, in a table in the library," Sherlock muttered. He tapped his thestral tail-hair wand against his thigh, and it sparked slightly in his excitement. "The third one, again outside the Ravenclaw common room, and a fourth in a seventh-floor corridor."

"I don't know what it could be about," Soo Lin said anxiously. "All I know is it's not good. I just...I get a funny feeling when I see them, like something isn't right." She paused. "Do you know what I mean?"

"Yes. Intuition is one of the detective's most important tools," Sherlock said. He bent closer to the runes and motioned for her to do the same. "Look at how they're laid out," he said, pointing at the first message. "Each line of the message is made up of sets of runes. Pairs. This is some kind of code; whoever's writing these, they don't want just anyone to be able to read them. And this one - " he pointed out a rune pair at the end of all four messages - "is the signature. See, it's the only pair that's an exact match on all four sheets."

"What could it mean?" Soo Lin asked in a hushed voice.

"I'm afraid Molly Hooper will have to answer that for me."

Chapter Text

With Soo Lin's permission, Sherlock took the transcribed messages to Molly the next day. She and John met Sherlock in the main Hogwarts courtyard during morning break. Conveniently, Ancient Runes had just gotten out, so the old magical symbols were already on Molly's mind.

"Wow," she said quietly, taking the small sheaf of parchment from Sherlock. She shuffled through them for a moment, her dark eyes flicking back and forth across them. "Soo Lin said these were carved into walls and tables?"

"Yes."

"Whoever did this really knows runes, then," she said. "They're almost perfect, beautifully done."

"Maybe we can skip the waxing poetic," Sherlock said impatiently. "Can you tell me what they mean?"

Molly gave him an annoyed look, but squinted closer at the symbols. "Well, they're not exactly words," she said carefully. "They look similar to the runes we've been reading, but not quite. See, these little dashes and loops aren't like any words I've come across."

"So what d'you reckon they could be?" asked John. Sherlock noticed he'd taken out the small notepad he used to write down clues, and ultimately keep records of their cases.

Molly shrugged. "Maybe a different dialect, if such a thing exists," she said. "Mind you, we're only reading present-tense runes this year. I don't know how much I'll be able to do."

"Well, take them and give it your best shot," Sherlock said. "We were both going to the library anyway. We need to write that essay on the Shrinking Solution for Snape. Want to come?"

"Sure."

Ten minutes later found the three friends in the Hogwarts Library on the third floor. It was one of Sherlock's favorite places in the castle, with endless rows of towering, crammed bookshelves, long tables for studying interspersed among them. Dust swirled in the shafts of light beaming through the floor-to-ceiling windows, which commanded a grand view of the Forbidden Forest. Sherlock found himself smiling as he breathed in the scent of old wood and parchment and took a seat at one of the tables. John looked distinctly less pleased, flopping beside Sherlock and sighing as he dug out a roll of parchment for the foot-long essay.

Molly set down her bag and dug through it for a moment. "I should probably start at the easiest place," she muttered, pulling out a book from her bag: a rune dictionary. While the two boys' quills scratched softly at the parchment, Molly thumbed through the dictionary. Sherlock was fairly absorbed in answering Professor Snape's assignment - "Describe the properties of the Abyssinian Shrivelfig and its role in the Shrinking Solution" - but every once in a while his ear caught an irritated huff from Molly's side of the table.

As Sherlock read his first draft, marking a sentence here and there for revision, Molly cast the dictionary aside. "Bloody hell," she muttered to no one in particular. As she dived back into her bag, John gave a snort loud enough to earn them a withering look from Madam Pince, the ancient, vulturelike librarian. Molly pulled out a second book, Ancient Runes Made Easy, and delved back into her work.

It was a bit more revealing than the dictionary. After another fifteen minutes of quiet searching, she reached over and tapped John and Sherlock's arms. "Here," she said. Pointing at a page, she read softly, " 'The pentimal system is a notation for presenting numbers, usually by inscribing in wood or stone, and generally in conjunction to runes. While outside the sphere of basic reading comprehension that is the purpose of this book, a study of the pentimal system is highly recommended for anyone hoping to become fluent in runic reading.' The footnote says, 'The author suggests the Spellman's Syllabary for an effective introduction to the pentimal system."

"Good," Sherlock whispered. "Find that book."

Chapter Text

After discovering the pentimal system, Molly promised Sherlock she would investigate the Spellman's Syllabary. The following afternoon at lunch, she approached the Slytherin table, looking most put out. "I talked to Madam Pince this morning during break," she said, throwing herself into an empty seat beside Sherlock. Several other Slytherins glared at her, but to her credit, it didn't seem to bother her.

"And?"

"And nothing," she said huffily. "The library has only one copy, and one of the sixth-year rune students has it out. And it's in the Restricted section on top of that! I'll need a note from Professor Babbling, and Madam Pince said the book wouldn't be back until the middle of next week."

Sherlock sighed. Today was only Tuesday. But he still gave Molly a thin smile. "Well, we've done all we can do for now."

He turned out, to his surprise, to be slightly wrong. Just as he and Molly were leaving the lunch table, a Slytherin second-year came up to Sherlock, a tightly rolled scroll in her hand. At the sight of the yellow fringes on Molly's robes she scowled openly. "Here, Holmes," she said shortly, thrusting the parchment at him. "Professor Wilkes asked me to give this to you after class."

Curiosity welled in Sherlock's mind, making a kind of soft hum. What could the Defense Against the Dark Arts professor want him for? He slit open the parchment and felt his own eyes widen at its contents. "We need to find John now," he said to Molly. The two of them raced over to the Gryffindor table, and Sherlock tugged at John's robe sleeve. "Professor Wilkes wants to see us," he said.

John and Molly looked stunned as Sherlock led the way out of the Hall. "What for?" asked John.

Sherlock read the message, occasionally stumbling on a stair on the way to Professor Wilkes' office. " 'Holmes, I would be greatly obliged to you if you would visit me in my office just after lunch. A curious matter has come up which you, given your interest in puzzles, may be able to help me with. (Your friend John Watson's serial has not only reached students' ears.) It is a matter to which I am inclined to give little importance, and thus I am not going to other staff members at this time. Sincerely, Professor Sebastian Wilkes.' "

"Hmm," said Molly. Neither she nor John seemed able to think of anything more to say, for they reached the Defense Against the Dark Arts teacher's office without speaking again. With some anxiousness, Sherlock knocked on the heavy wooden door.

A man in his early thirties, with neatly parted brown hair and a mischievous twinkle in his eye opened the door. "Ah, Holmes," said Professor Wilkes. "And your friends are...?"

"John Watson and Molly Hooper, sir," Sherlock said. His friends each nodded as he said their names. "Don't worry, whatever you have to say to me can be said in front of them."

"Naturally," said the professor, smiling at the three students. "Please come in." He opened the door wider, and they entered a small, but comfortable office. Ungraded student papers and tests sat in a neat pile on the desk, with an eagle-feather quill and a wand lying beside them. Books filled the shelf lining the left-hand wall, books with titles like Confronting the Faceless and The Big Book of Jinxes, Curses, and Hexes. As there was only one chair in front of the desk, Sherlock, John, and Molly all remained standing.

"Well, Holmes, as I said in my message, I've invited you here for a puzzle," said Professor Wilkes. A crooked smile crossed his face, a pleasantly disarming trait that, Sherlock knew, led more than one Hogwarts student to fancy the man. "I've had a bit of a break-in. Last night the Intruder Charm I put on my office door went off. It went silent just after I arrived to investigate, about a minute after it was triggered. That means whoever was in here got in and out in less than one minute."

"Was anything stolen?" Sherlock asked. Beside him, John was quietly taking notes.

"No," said the professor. He got up and walked around the desk, to the still-open door. "I assume it was just a student playing a silly prank. But they left a kind of message." Pushing the door closed, Professor Wilkes pointed at the wall. Sherlock heard the softest of inhales from Molly.

Etched into the wall, so precisely that it had to have been done with a wand, was a pair of symbols from the pentimal system.

The three students approached it. It was one of the symbols Soo Lin Yao had provided, the "signature" at the end of each message she'd transcribed. The markings were flawless, and Sherlock recognized the near-perfect roundness each loop had. Even when someone used a wand to write, their handwriting was still completely unique. Sherlock took out the summons from Professor Wilkes and copied them down, noting the date and location as Soo Lin had.

"It looks like this message was meant for you, and only you," Sherlock said. "No one else but you would see it. Does it mean anything at all to you?"

"Not a thing." Sherlock glanced up at the professor. His eyes, mystified as they fell again on the symbols, showed that he was being honest. The professor was likely not involved with whoever was writing the runes; the writer just thought he was. Sherlock pocketed the copy.

"And what do you want us to do?" John asked politely.

"Find whoever did it," said Professor Wilkes simply. "I would offer to pay you, but that kind of private transaction between a professor and a student might be frowned upon."

"I understand," Sherlock said quickly. "You can count on us, Professor."

Professor Wilkes smiled. "Thank you, Holmes. And thank you, Watson and Hooper." He showed them out of his office, adding, "And don't forget to bring your wands to next week's lesson. We're doing a practical on boggarts."

Chapter Text

Following the conversation with Professor Wilkes, there was not much left that Sherlock and his friends could do to move the case forward. The Spellman's Syllabary was still checked out of the library; Sherlock had asked Molly not to bring the messages to older Ancient Runes students who might be able to read them.

"Soo Lin asked us to keep her connection to these messages quiet, so we will," he told Molly one day in Herbology. Today they were reviewing relatively calm plants, Puffapods, which made it a good lesson to talk about the case. "Besides, even if she hadn't asked, it would be a good idea to not parade what we're doing."

"Do you think whoever's writing these messages might be dangerous?" Molly tried to keep her voice calm, but the shiny pink beans they were stripping from the plants rattled slightly in the bowl she was holding.

"It's certainly a possibility."

"Sherlock, it's okay to admit it when you don't know."

Sherlock rolled his eyes, but felt a little grin tug at the corner of his mouth. "Fine," he said. He let a handful of beans shower into the bowl. "I don't know yet. That's why I think we should keep this as quiet as possible, in case they are dangerous."

Luck finally favored them on Wednesday. After their Ghoul Studies session, Molly walked straight to the library, while Sherlock and John went to the Great Hall to load up plates. John, ever thoughtful when it came to food, piled shepherd's pie on a plate from the Hufflepuff table. Just as they were sitting under their usual tree on the grounds, Molly appeared in the castle doors, a book the size of a paving slab in her arms. She joined the boys, and Sherlock could swear he saw the branches above his head shake from the book's impact as she set it down.

"Here it is, at last," Molly puffed, taking her plate. "Thanks for getting me some food." She started to open the Spellman's Syllabary while holding a fork in her other hand, but Sherlock held it shut.

"Let's eat first," he said. "Then we can look at the book." John and Molly shared a surprised glance, and for good reason. Sherlock almost never put food before a case. But, unknown to the other two, his stomach was rumbling and distracting him. He was a growing thirteen-year-old, after all. The three of them ate in near silence, bathed in the cool green shade from their tree's branches.

When they'd finished eating, Molly heaved the Syllabary open. Running a finger down the table of contents, she found the section on the pentimal system. The three of them bent over the page and read:

" 'The pentimal system, while not runic in the most traditional sense, is still of value to anyone wishing to become fluent in ancient runes. This writing system is similar to Roman numerals for numbers up to 9. The digit is indicated by the number of ticks attached to the runic base. From numbers 5 to 9, an inverse "u" marking is attached to the base, with as many ticks following as necessary (for example, 8 would be notated with a "u" and three ticks). The system, while clear from numbers 1-9, becomes unwieldy for numbers beyond 10, for the symbols for 10 and 0 are the same. The pentimal system is impractical for complex calculations, and there has been much confusion over which year wizards in the Middle Ages meant when they used this notation.' " Below this paragraph was the array of symbols used in the carved messages.

"Numbers," Sherlock said quietly. He pulled Soo Lin's transcribed messages, and the one he'd found in Professor Wilkes' office, out of his pocket and spread them out. "Pairs of numbers."

"Let's see what those numbers are, shall we?" said John, his face shining with excitement. He pulled out his trusty notebook, and wrote each pair of pentimal numbers in the first message out neatly. "Hit me."

Molly smiled at his enthusiasm and bent over the picture in the Syllabary. "The first one is 9, 3." She paused as John wrote the first pair underneath the pentimals. "Second..." Molly paused and pointed at the next pair. "Sherlock, what d'you think about this one? There's more than one rune for each number."

Sherlock thought for a moment. The pentimal symbols for 0/10 and 7 were side by side. "Well, if the writer wanted a seven, wouldn't they have just written seven? I think this means seventeen." He looked at another number set, where there were two numbers for each side of the pair. "And here, we've got six and nine together, paired with two and three. The writer could've just written 10/5 and 5 if he wanted fifteen and five."

"So those mean sixty-nine and twenty-three," John chipped in, scribbling the numbers down. In this manner, they continued working, until they'd translated the first message into Arabic numerals.

Unfortunately, they didn't get much farther on the decoding than that. Sherlock heard running footsteps coming towards them, and all three students looked up to see Soo Lin Yao dashing full-tilt across the grounds. "Good, you're here," she gasped, clutching at a stitch in her side. "There's been another carving."

"What?" said Sherlock, dropping his fork with a clatter. "Where?"

"Somewhere in the library," Soo Lin said, her face pale. "My friend Charlie Lucas found it, he told me. He's in the hospital wing. Someone tried to use a Slashing Curse on him when he saw it."

Chapter Text

Sherlock, John, and Molly dashed after Soo Lin all the way up the lawns and to the hospital wing. Madam Hudson, the Hogwarts matron, reluctantly let them in. "The patient really should be getting some rest, not discussing what happened," she said. "But, as it seems so important to you, I suppose a brief visit won't hurt."

"We won't be any more than ten minutes," Sherlock promised. He saw a smile on the kindly older woman's face. He knew she remembered Mycroft from his Hogwarts days, and as Mycroft had gotten her out of a tight spot, she looked kindly on his little brother.

"Very well," said Madam Hudson. "Lucas is over here." She led them to a bed at the very end of the ward and pulled back the curtains. Sherlock contained a gasp, something that Molly wasn't so successful at.

Charlie Lucas, a Ravenclaw seventh-year, had been brutally attacked. Deep red welts crossed Lucas' round face, and under his pajamas Sherlock could see the thick pads of bandages. The Slashing Curse must've cut his torso and arms as well as his face. Sherlock had never used the curse before, and now that he saw its effects, prayed he'd never have to.

"We're sorry to bother you," Molly began, but Lucas shook his head slowly.

"No, it's all right," he said in a low, exhausted voice. "Soo Lin says if anyone can help find who did this, you three can."

"So you've no idea who cast the curse?" Sherlock asked. John started to pull out his notebook, but Sherlock shook his head slightly at him.

Lucas shook his head too. "It wasn't a voice I recognized," he said slowly. "I was in the library, in the advanced Transfiguration section. I pulled out a book and I was looking at it when I heard someone yell 'Sectumsempra.' Next thing I remember was waking up here."

Lucas' voice was calm and steady as he recounted the attack. But Sherlock, who'd heard it from Soo Lin, knew that Lucas was omitting the runic symbol in the library. At least he'd told them where they could find it. "We'll do our best to help find whoever cast that curse," Sherlock promised. "But was the voice a man's or a woman's?"

"A man's. But he didn't sound that old." At that moment, Madam Hudson's hired assistant Poppy Pomfrey bustled over, carrying a goblet that was smoking slightly. From the smell, Sherlock knew it was essence of dittany, to heal cuts and prevent scarring.

"Thank you," he said to Lucas. "We'll let you rest." Lucas nodded, and as he took the goblet from Poppy Sherlock led the way out of the hospital wing.

As soon as they were out the door, he turned to Soo Lin. "Lucas told us where he was when he was cursed," Sherlock said. "We need to go there right now and look at the symbol." The other three looked anxious, but charged up to the library after Sherlock.

Upon arriving at the advanced Transfiguration section, Sherlock faced the group. "We know he was here, looking at a book, but we don't know which shelf. We need to split up. I'll take this shelf here." He gestured to the shelf on his immediate right. Molly, Soo Lin, and John all nodded and fanned out to the other three advanced Transfiguration shelves.

They'd only been searching for a moment when John's voice floated above the shelves. "Sherlock," he said in a soft, shocked tone. Sherlock and the two girls found John, who was standing with a pile of removed books in his arms, staring nervously at the shelf. They gathered around him to look, and as a course of excitement surged through Sherlock's veins, the thestral-hair wand in his pocket glowed slightly.

Carved neatly and precisely into the old wood was the same symbol he, John, and Molly had seen in Professor Wilkes' office, and at the bottom of Soo Lin's messages.

Not speaking, he copied it, with a date and location, onto a spare bit of parchment Soo Lin pressed into his hand. The four third-years left the library, before Filch came in and caught them snooping at the scene. Turning to Soo Lin, Sherlock said, "It's the writer's signature. Whatever he was trying to say to Professor Wilkes, he wanted to say it to Lucas too."

Soo Lin went pale. "Do you think they're dangerous?"

"It led to Lucas getting cursed, so yes, I think they're dangerous," Sherlock said grimly. "The signature is the pentimal numbers fifteen and one. I don't know what it's supposed to mean yet, but I have an idea. In the meantime, be on your guard and tell us the instant you see another of these messages, or this signature."

"Why?"

"Because," said Sherlock as they walked into the Entrance Hall, "something tells me this person wouldn't be very happy if they knew any of us were on to them."

Chapter Text

Sherlock and his friends continued to keep their eyes peeled for more runic messages. However, the writer seemed to be taking some time off. For the rest of the week, none of them found any more pentimal symbols around the castle. Sherlock was racking his brains, trying to think of a reason this person needed to use a code. Obviously, the topic of the messages was highly secret, and there were at least two recipients: Professor Wilkes (though he hadn't recognized the symbol in his office) and Charlie Lucas. And, as Lucas was currently recovering from the Slashing Curse, the message writer clearly meant business.

They could only conclude that the writer and Lucas were part of some kind of group. What the group's purpose was, or how large it was, Sherlock had no idea. Only decoding the messages would tell them that, and so far they'd uncovered half of the puzzle. They knew the code was comprised of number pairs, but that was all. That left him with the question: what sort of code organized numbers in that particular way to form words?

Sherlock was still pondering this over Friday's Defense Against the Dark Arts lesson. As promised, Professor Wilkes captured and contained a boggart for the class to learn about. Before the session began, they had a short discussion of the shapeshifting creature, learning how they changed shape depending on what an individual person was most afraid of. Sherlock was only half listening; Mycroft had dealt with a boggart in the Holmes house, under the kitchen sink, last summer. Sherlock already knew what his own boggart was, for he'd been the one who found it. He shivered slightly and, hoping no one had noticed, went back to puzzling over the code.

"Now," said Professor Wilkes, taking out his wand. "I realize that facing your greatest fear can be a difficult and very private act. So, if all of you will wait outside, I will call each of you in to face the boggart with only me in the room. I give you my word that I won't repeat what I see," he assured them with a slight smile. "Philip Anderson, you're first." Anderson stayed in the classroom while the other third-years shuffled out into the corridor.

Sherlock's turn came all too soon. He pulled out his wand and walked into the classroom, where Professor Wilkes was standing beside an old wardrobe. "Now, Holmes, what is the incantation?"

"Riddikulus," Sherlock said.

Professor Wilkes nodded. "And remember, what really finishes a boggart is laughter. Force it to assume a shape you find amusing."

Given what his boggart was, Sherlock had no idea of how to make it funny. How could something so awful be anywhere near funny? But he nodded anyway and rolled up his robe sleeves. In the split second before the wardrobe door opened, a glimmer of an idea came to him, inspired by a brief mention of Dementors in Fantastic Beasts and Where to Find Them.

Professor Wilkes tapped the handle of the wardrobe and Sherlock gripped his wand tighter as what stepped out was...himself. But his face was pale and drawn, and the look in his own eyes was one he recognized all too clearly. It was the deep, penetrating sorrow that came from being alone, with no friends at all. A shudder of fear went through him, but Sherlock held the boggart's gaze and focused as hard as he could on a mental image of John and Molly's faces. "Riddikulus!" he shouted. There was a loud crack and the boggart suddenly split into three people: himself and his two friends laughing together. Professor Wilkes waved his wand and the boggart was forced back into the wardrobe.

"Very good, Holmes!" cried Professor Wilkes. "That's the first time I've ever seen a boggart repelled by positivity and not laughter. Well done." As Sherlock exited the room, flushed with his success, Molly went into the room next. She was only in there for a few minutes before she came dashing back out, pale as death, and ran all the way up the corridor and out of sight.

After the lesson, Sherlock ran up to John in the corridor. His friend looked pleased. "I beat it," John said proudly. "Somehow I turned a nuclear bomb into an Exploding Bonbon."

"Great. I beat it too," Sherlock said. He was keen to change the subject before John asked about his boggart. "We need to find Molly and talk. I think I have an idea about the code, about how we break it."

The boys found Molly at the Hufflepuff table, preparing to load up on dinner. While she was still pale, she seemed to have recovered from the boggart. Sherlock and John got their own plates and the three went onto the grounds to discuss Sherlock's idea. It was a lovely evening: the setting sun's golden light glinted off of the castle windows and greenhouses.

As they sat down together, Sherlock jumped straight in. "I think I know what we need to do next about the code," he told Molly and John. "It's pairs of numbers, right?"

"Right," they both said at once.

"Well, what kind of source would have enough numbers to make that many pairs?" When neither of his friends responded, Sherlock said, "How about a book?"

John's face lit up. "That makes sense!" he exclaimed.

"So what exactly do the numbers refer to?" Molly asked. "Chapters? Pages?"

"My brother Mycroft told me about book code once," Sherlock explained. "The first number refers to a page, and the second number refers to a word on the page. So the signature, fifteen and one, means the first word on the fifteenth page."

"But the message would depend on what book was used to generate the code," Molly pointed out.

Sherlock nodded. "That's why we'll need to talk to both Professor Wilkes and Charlie Lucas again," he said. "We need to have a look at their books."

Chapter Text

Over the weekend, Sherlock went to both Professor Wilkes and Charlie Lucas to ask about their books. Both of them, were, understandably, mystified. Nevertheless, they agreed to let Sherlock and his friends examine their collections. Sherlock took the liberty of reminding them that the search would help right both their wrongs.

"Very well," Professor Wilkes told him. "Come to my office this evening and take them. Just make sure you return them to me by Monday." Lucas, for his part, agreed to let Soo Lin take his books out of his trunk. By Saturday evening, just after dinner, Sherlock was meeting John and Soo Lin in the Slytherin common room. Both of his fellow students were levitating stacks of books with their wands. But there was something missing from the meeting, and it only took Sherlock a moment to work out what it was.

"Where's Molly?" he asked Soo Lin.

"The Defense Against the Dark Arts classroom," she replied. She waved her wand and the book stacks drifted neatly to the floor. "She wanted to have another go at that boggart."

"Does Professor Wilkes know she's in there?" John asked.

"No."

Sherlock doubted the wisdom of Molly's decision, but there was nothing he could do about it right now. He figured she would be all right for now. He glanced at John, who waved his wand like Soo Lin. Unlike hers, his stacks of books collapsed to the floor in heaps. He grinned shiftily, his tell for embarrassment. "Sorry," he muttered.

Sherlock shrugged to say it didn't matter, and moved towards the heaps of books. "As long as they didn't get mixed up," he said.

"No," said Soo Lin. She pointed at her neat stacks. "These are all Charlie's books. Professor Wilkes' are all over there by John."

"What do we need to do?" John asked Sherlock.

"Well, Professor Wilkes and Lucas were both contacted with the same code," Sherlock told them. "For both of them to decode the messages - the writer thinks Professor Wilkes is involved, remember - the messages would all have to be taken from the same book."

Soo Lin looked thoughtfully at Lucas' books. "So we're looking for a book they both own?" she said.

"Right. We'll need to isolate those first and then look at all of them. We're looking for a shared book that yields a message that makes sense."

"Well, this shouldn't take too long," John said sarcastically. Sherlock smiled and the three set to work. It was painstaking, agonizingly slow. If there was a spell that would sort the books in the way they wanted, none of the three third-years knew it, so they searched manually. Thankfully, as a student, Lucas had far fewer books than Professor Wilkes. After about an hour and a half of careful looking, they'd gone through the seventh-year's stack and pulled out anything he had in common with the professor. About six or seven pairs of books sat around their feet.

Soo Lin sat back on her heels, rubbing her eyes. Seeing this, Sherlock said, "You can go if you like, Soo Lin. John and I can finish."

"Thanks," she said quietly, getting to her feet. She left the dungeon common room for her own dormitory in Ravenclaw Tower. In the brief silence that followed, John turned to Sherlock. "So what now?" he said.

"We finish writing down the pentimal numbers first," Sherlock said. He pulled out the stack of message transcriptions and laid them out on the emerald rug. "Then we look at the books and see which message makes the most sense." John nodded, and pulled the nearest two books to him: a Defense Against the Dark Arts textbook, Confronting the Faceless.

After a moment, Sherlock slapped his forehead. "Stupid, stupid," he muttered.

"What?"

"The Spellman's Syllabary," he said. "Molly's the only one of us who has a copy. I'll have to go get it from her. Hope she's still in the classroom."

"Finish this tomorrow, then?" John said, looking at his watch. "It's a quarter to nine. I need to get back to Gryffindor Tower or Filch will skin me alive."

Sherlock nodded, and the boys left the common room together. In the Entrance Hall John turned to go up the sweeping staircase, and Sherlock proceeded to the third floor. The castle was nearly silent; only a handful of older students, whose curfew was ten o'clock, could be seen walking around. Sherlock was not nervous, as curfew didn't end for another few minutes. He strode up to the Defense Against the Dark Arts classroom and knocked on the heavy wooden door. Molly didn't open it, and he wondered briefly if she'd already left.

But then he heard a quite unexpected sound. It was a sort of soft whimpering and groaning, and it was coming from behind the door. Pulling out his wand, Sherlock tried the handle and found it unlocked. Carefully, he eased it open.

Moonlight shone from the high windows, casting strange shadows on the desks and dragon skeleton hanging from the ceiling. He could just make out a shivering, sobbing form on the floor, near the old wardrobe the boggart lived in. And sprawled on the floor, their eyes blank and empty, their faces white as death, were a man and a woman. The woman had long, straight, blond-brown hair, and the man's blank eyes were dark. Sherlock felt his heart miss a beat: it was Mr. and Mrs. Hooper.

But wait, that didn't make sense. The Hoopers were back in Sussex...

"Molly?" Sherlock said, and he was surprised to hear his voice come out in a croak. He came closer, but she didn't seem to hear him.

"Riddikulus," Molly muttered, crying, pointing her wand at the corpses. The slim, beautifully carved pear branch was shaking violently. There was a loud crack, and Molly's parents turned into Soo Lin Yao, her eyes also lifeless and empty. Molly gave another anguished sob.

"Riddikulus! RIDDIKULUS!" she cried again. Sherlock watched, horribly mesmerized, as the boggart transformed into John, his neck twisted at an odd angle as if it had been broken. Then, with the loudest crack of all, it replaced John's body with a long, lanky teenager, blood trickling down his face from a deep gash under curly, dark brown hair. Molly gave a scream of despair and her wand clattered to the floor.

Sherlock was staring at his own corpse.

It was time to act. Knowing the boggart would be confused if confronted by both of them, he stepped forward and helped Molly stand. Sure enough, it transformed into a still bloody, but walking and desperately lonely, version of himself. Sherlock shot sparks at the boggart and, frightened, it turned into a wisp of smoke and zipped back into the wardrobe, which Sherlock locked. Taking Molly by the arm, he led her out of the classroom.

They didn't speak at all. Sherlock could still see tear tracks glittering on Molly's cheeks in the moonlight. He walked her down to the Hufflepuff dormitory down by the kitchens, just as she had once walked him down to his own common room. They stopped in front of a large pile of barrels tucked into a small recess off the corridor. On the wall just outside the recess was a large painting of a pretty lady with coppery blond hair and kind, blue-green eyes. From the finely carved frame around it, masterfully worked in gold leaf and black onyx, Sherlock concluded this must be Helga Hufflepuff, the House's founder. She blinked curiously at the red-eyed Molly and the stranger accompanying her, but said nothing.

Turning to Molly, he opened his mouth, wondering what on earth he should say. But she stopped him. "Thanks, Sherlock," she said quietly, not looking at him. She bent over the barrels, tapping out a rhythm on a particular one. The front of the barrel swung away with a creak, revealing a hole in the stone wall and a low, earthy passage sloping upward. Sherlock caught a glimmer of gold from the top of the passage before Molly went inside and the door swung shut.

Sherlock tried to ignore Helga Hufflepuff's smirk as he passed her portrait on the way back down the kitchen corridor. His mind was coming to grips with the scene he'd just witnessed. Molly's boggart was her loved ones, dead on the ground before her, and Sherlock's head reeled slightly at the fact that his corpse was on that list.

Chapter Text

The next morning, Sherlock and Molly acted, as if upon mutual agreement, as though the incident in the Defense Against the Dark Arts classroom had never happened. Sherlock knew his friend was deeply embarrassed, and he was not keen to delve into the topic himself. It was a relief when, after breakfast, she accompanied him and John back down to the Slytherin common room. Work, he knew, would keep both of their minds off of it.

"First, we need to translate the numbers," Sherlock explained to Molly. She nodded as she hauled the Spellman's Syllabary out of her bag and plopped it onto a table. "Then, once we have the numbers, we work out which book they came from."

"At least you and John and Soo Lin narrowed it down," Molly said, nodding at the pairs of books set aside. "Once the numbers are all in, it shouldn't take too long between three of us."

She turned out to be right. Translating the pentimal symbols into Arabic numbers took most of the morning, but they were lucky with the books. The first sets yielded completely nonsensical words for the message writer's signature: "cigarette" and "imagine." But the third book, A History of Magic by Bathilda Bagshot, was where they struck gold.

"Sherlock," Molly murmured. The boys bent over the old book, looking at the first word on the fifteenth page. Bagshot was describing the site of the first documented Killing Curse, a place in Surrey called Deadman's Grove after the incident.

" 'Deadman,' " Sherlock said, his voice almost a sigh. He closed his eyes, seeing the pentimal numbers fifteen and one behind the lids. "So he was threatening them."

"And apparently he does a lot of threatening. He uses it to sign the other messages," John pointed out.

"Let's see what all of these things say, shall we?" said Molly. She took up the first message and placed it next to the book. Sherlock and John watched in silence as she turned pages slowly, running a finger down the old paper as she found each word. She carefully notated each word underneath its pentimal symbols and translated Arabic numbers.

Finally she spoke. "Here's the first message. 'Arrived at Hogwarts. Searching for diadem. Raven's nest shack, Hogsmeade.' What do they mean by diadem?"

Sherlock's brain was whirring. He handed the next missive to John, who set to decoding immediately. Sherlock explained to Molly, who was Muggle-born and wouldn't have heard the story. "The lost diadem of Rowena Ravenclaw. It's supposed to bestow wisdom on the wearer. Someone's been sent here to search for it; raven's nest must mean their meeting place, the Shrieking Shack. If they found the diadem, it would be priceless."

"So you think they want to sell it?" said Molly, flabbergasted.

"Yes," said John. He read out the next decoded message. " 'Have searched, not in Ravenclaw Tower. Meet in raven's nest for discussion.' "

The third and fourth messages didn't take long to translate. The third one, which had been carved outside the Ravenclaw common room, reported a possible location for the diadem and requested time to investigate. The fourth message, from a seventh-floor corridor, was only two words long: It's here. When Molly finished decoding the fourth message, her eyes grew huge. "They actually found it?" she said incredulously.

"It seems so," Sherlock said. In his pocket, the thestral-hair wand glowed bright yellow from his excitement.

"But you know what this means, right?" John said urgently. "These people are trying to steal something historic and sell it. We have to stop them."

"But how?" said Molly. "We don't even know who's doing this, let alone when they're going to try and steal the diadem."

Sherlock would never admit it, but he was at a loss. "Well, at least we know where in the castle they're planning to strike," he said, pointing at the fourth message. "We can do our best to keep an eye on it, maybe get one of the ghosts to help. We don't have to explain it that well, they generally don't ask questions. And we need to tell Soo Lin about this right away."

"I'll go and find her," Molly volunteered.

"The password's 'bat's wool,' " Sherlock said. Molly nodded, and she left the Slytherin common room. The boys started putting the books back into their respective piles, to be returned to Professor Wilkes and Charlie Lucas. Once they were finished, they settled into two chairs near the fireplace to wait for Molly and Soo Lin.

They didn't have long to wait. About ten minutes after they'd finished resorting the books, Sherlock heard running footsteps out in the dungeon corridor. The stone entrance slide aside, and Molly dashed through the doorway. His heart sank: she was alone. "What happened?" he said, standing as his friend skidded to a halt in front of him. "Where's Soo Lin?"

There were two bright patches in Molly's cheeks from exertion, but otherwise she was pale as death. "I looked everywhere in Ravenclaw Tower," she said, her voice low and flat with shock. "I couldn't find her. And this was carved into her bed's headboard, right where she'd see it." She held out a small scrap of parchment. John and Sherlock bent over it, both dreading what they'd see there.

In Molly's small, neat handwriting were the pentimal numbers fifteen and one: Deadman.

Chapter Text

Sherlock, Molly, and John had to wait until the evening before they set off in search of Soo Lin. Her absence in class was not commented upon, though Sherlock knew the professors had noticed it. A little crease had appeared between Professor Flitwick's eyes when he read her name and didn't get a response. All day the same question bounced around in Sherlock's head: What did Soo Lin have to do with any of this?

It was a relief when, at last, dinner was over and all the students had retired to their common rooms. Sherlock met John and Molly in their usual classroom off the Entrance Hall. As John closed the door behind him, Sherlock wasted no time. "Did you see her at all?" he asked Molly.

"No," she said in a small, scared voice. Her eyes were red and swollen, and Sherlock felt a little tug of sympathy in his chest. Soo Lin was one of Molly's closest friends, he knew.

"Well, we'll just have to go and find her, then," John said. Sherlock nodded and pulled out the little stack of decoded messages.

"This one was in a seventh-floor corridor," he said, pointing at the final, brief message: It's here. "I know it's not much to go on, and it might not help us find Soo Lin, but I think we should look into it all the same." Molly and John nodded in agreement, both of them drawing their wands.

Sherlock led the way through the castle. On the surface, it was a perfectly ordinary spring evening. The warm gold sunlight of late afternoon streamed through the windows, seeming to light Hogwarts from the inside. Down on the grounds, he could see students lying under trees and milling around the lake, enjoying the lengthening days, not a care in the world. At this moment, filled with apprehension about Soo Lin, he envied their boring lives. Neither he nor his friends spoke through the long walk up to the seventh floor.

After what seemed like an eternity, they reached the main corridor. It was completely deserted, aside from the ghost of a long-haired woman who drifted past without a glance at the three students. Pulling out his wand, Sherlock turned to the other two. "Spread out and look for the message," he said. "See if there's anything strange or out of place, anything at all that might help us." Molly and John nodded, and the three fanned out across the corridor, Sherlock going left, the others going right.

Sherlock found the carved message, near the end of the left-side corridor. The runes, scratched neatly into the stone with a wand, matched the symbols on the piece of parchment. It was next to a large tapestry showing a bunch of trolls in ballet outfits, chasing a hapless-looking wizard. Sherlock pushed the tapestry aside, but there was nothing there except a blank stretch of wall. He paced up and down in front of it a few times in frustration, his mind on Soo Lin, wishing he could find her and wondering where she might have hidden.

Just as he was turning away to call John and Molly over, he heard a strange grinding sound behind him. He turned; the blank stretch of stone across from the troll tapestry was moving. The large chunks of gray stone were quivering, transforming before his very eyes into wood. Transfixed, he watched as the wood solidified, stopped quivering, and became a plain door.

"Sherlock?" Molly's voice reached him from further down the corridor. "Did you find anything?"

"I think so," he called back, keeping his eyes on the door in case it disappeared again. "Come here and have a look."

When John and Molly arrived at his side, they both gasped. "What...?" John began to ask.

"No idea," said Sherlock. "I was just thinking about Soo Lin when this door appeared."

"Let's see what's in it, then," Molly said. Before either of the boys could say anything, she opened the door and they followed her inside. Sherlock gasped: he'd never seen a room like this in his life.

They were standing in a room the size of a cathedral, filled with mountains of objects. All Sherlock could think was that this must be centuries' worth of hidden things. There were towers of broken furniture, heaps of robes and scarves and cloaks, moth-eaten tapestries and rugs that were once quite fine dangling from every wall and covering the floor. Quidditch supplies - broomsticks, Quaffles, a Snitch with a bent wing that still hovered lazily - lay in odd piles in corners. Paintings, statues, and frames stood like sentinels, and in the distance Sherlock could hear a scratchy old record playing the same three bars of an aria over and over. Between these mounds of hidden treasures were small pathways, like streets between towering city buildings.

"Split up and look for Soo Lin," Sherlock said. He found himself whispering, as if the previous owners of the room's treasure could hear him. "Send up red sparks if you find her." Wands out and looking very serious, Molly and John split off along the left- and right-hand paths. Sherlock took a deep breath and walked alone down the middle.

The longer he walked, the more treasures the room yielded. He passed thousands of books: graffitied, banned, stolen. Open trunks yawned wide, showing their contents; one of them glistened with jewels. He passed a large, heavy black cabinet with gold trim around the edges, and several empty cages, one of which still contained a 5-legged skeleton. Part of him wondered if Mycroft had known about this incredible room. But as fascinating as it was to walk between walls of history, he was worried: Soo Lin was nowhere to be found. He wanted to call to her, but the silence in the room made him nervous and uneager to give away his position. For all he knew, someone else could be in the room besides him, John, and Molly.

Then, as he passed a massive stuffed troll, the silence was broken. Sherlock froze: a soft snuffling, rather like the noise a wounded small creature might make. The thestral-hair wand in his hand glowed at the sound of it. It seemed to be coming from behind one of the towering piles of broken furniture and discarded Quidditch items. Wand held out in front of him, Sherlock came around the corner.

There, leaning up against a blistered cabinet that seemed to have had acid thrown at it, was Soo Lin. She looked dreadful: her black hair hung lank and unwashed around her face, which was currently red and swollen from tears. As Sherlock stepped towards her, his foot landed on a piece of a broken wand, and the snap made Soo Lin jump to her feet, wand drawn.

"No, Soo Lin," Sherlock said, "it's okay, it's me."

Soo Lin didn't say anything, but her bottom lip trembled. Next thing Sherlock knew, and to his great discomfort, she was in his arms, her shoulders shaking with quiet tears. Awkwardly he patted her on the back.

"John and Molly are here too," he said, not knowing what else he was supposed to do. "Soo Lin, why are you in here?"

"So he won't find me," she gulped into Sherlock's robes. "He was coming for me."

"Who?"

But before Soo Lin could answer, a deep voice said quietly behind Sherlock, "Me."

Chapter Text

At the sound of the stranger's voice, Sherlock and Soo Lin broke apart, both wands raised. Sherlock turned to face the newcomer. A young man, no more than nineteen or twenty, emerged from behind the nearest stack of broken furniture, his own wand pointing directly at the two third-years. He was not much taller than Soo Lin, with a semi-square jawline and identical straight black hair. His dark eyes gleamed, but had no trace of Soo Lin's warmth. As Sherlock took in his appearance, he noticed a tiny mark on the man's right wrist: what looked like the tip of a bird's wing.

"I thank you for leading me right to her, Holmes," the man said, a chilling smile curling the thin lips. "I think she has information I might find helpful."

"Oh, really?" said Sherlock coldly. He moved an inch or two to the left, so he was in front of Soo Lin again. "And what kind of information might that be?"

"You know perfectly well. You and your little friends have been working on my code, after all."

"You want to find Ravenclaw's diadem," Sherlock said quietly. His heart was pounding, but his wand hand was remarkably steady. The other man laughed.

"Very good. You and your friends deserve House points for your detective work." He laughed derisively.

Sherlock's mind was racing. This stranger obviously knew Ravenclaw's diadem was somewhere in this room, and thought that Soo Lin could help him find it. How could he, Sherlock, get his friends out of this and keep the man away from the diadem at the same time? Nothing was occurring to him, and in the silence Soo Lin spoke in a small, but determined voice.

"Jing Li, if you want help I can't give it to you. I don't know where the diadem is."

Jing Li's face darkened. "You're here in its hiding place, aren't you?" he growled at her, trying to point his wand at her around Sherlock. "You were part of the search, weren't you?"

"I was," she said defiantly. "That's over now."

Before Sherlock could ask for an explanation, John's voice floated over the mounds of furniture from the alleyway next door. "Sherlock? Are you talking to someone?"

Jing Li's wand moved so quickly Sherlock had no time to react. "Descendo!" he roared, and the nearest pile of heavy books, broken chairs, and old trunks toppled into the alleyway where John stood. Sherlock heard a scream from the other side of the room and a yell from the alley.

"Finite!" Sherlock cried, pointing his wand at the toppling tower. It steadied, but Jing Li turned to face Sherlock again and advanced, wand at the ready.

"I'll make it easy for you, boy," he snarled, an ugly look twisting his face. "Point me to Ravenclaw's diadem, and I spare your life, and possibly even your friends' too..."

"When hell freezes over," Sherlock said. "Petrificus Totalus!"

Jing Li dodged the Full-Body Bind Curse, but narrowly; the beam hit a trunk and caused it to spring open. A cloud of moths flew out of it as Sherlock grabbed Soo Lin's hand and made a dash for the exit. "Molly! John! Head for the door now!" he yelled, his voice echoing in the cathedral-like room. He and Soo Lin bolted through the alley, Jing Li's heavy footsteps pounding after them.

"Impedimenta!" Sherlock heard him roar. He dived behind a marble statue of an angel and heard the wing crack as the spell hit it. Soo Lin, after a quick glance back, kept running for the exit. Sherlock pointed his wand at Jing Li and did the first thing that popped into his head: shot a jet of water at him. Though it wasn't a curse or jinx, it caught him off guard. As Jing Li coughed and spluttered, Sherlock took flight again.

Next thing he knew, brown-blonde hair was flying in front of his face. Molly had hurtled out from between two tottering heaps of books to join the chase. As Jing Li began running again, she pointed her wand at Jing Li and shrieked, "Mobilicorpus!" To Sherlock's amazement, Jing Li was instantly suspended in midair, and as Molly flicked her wand, flung into a heavy bookcase and showered in heavy books. John hurtled out of nowhere and Sherlock thought he saw something glittering in his friend's hand, but there was no time to ask questions. The four students bolted around the corner and the door came into view -

"Locomotor Mortis!"

Jing Li's yell echoed in the high chamber and Sherlock heard cries as both Molly and John toppled behind him. Turning, he saw that their legs seemed to be stuck together; Molly's wand flew from her hand and skittered to a halt about twenty feet away. Jing Li grabbed Soo Lin by both arms, pinning them to her sides, and kicked John's wand away. "Now, boy," he growled at Sherlock, "give me that diadem."

Sherlock looked down at John. Sure enough, a small silver tiara with great blue sapphires and glittering diamonds set in it twinkled back at him. Having no choice, he bent down and took it from John's shaking hand. Slowly, he advanced toward Jing Li. His sleeve had been pulled up now, and Sherlock could see what was tattooed there: a tiny black raven. Jing Li's eyes gleamed with a hunger that made shivers go up Sherlock's spine.

Just as Jing Li reached out to take the diadem, a familiar voice sounded from behind Sherlock, one he hadn't heard since last year's case. "I wouldn't take that if I were you, mate." Before Sherlock could turn around to greet this welcome intruder, the voice cried, "Incarcerous!" Sherlock jumped out of the way as shining black ropes soared past him and wrapped tightly around Jing Li. Soo Lin walked away from the prisoner, shaking from head to foot, and muttered the countercurse to the Leg-Locker Curse. John and Molly stood, and Molly went to fetch her wand.

A whiff of stale tobacco and firewhisky hit Sherlock full in the face as he turned, but he'd never been happier to smell them. Before him, lowering his wand and pushing his straggly ginger hair out of his basset-hound eyes, stood his fellow Slytherin and a new Hogwarts graduate: Mundungus Fletcher. Mundungus grinned at Sherlock, and at the other three third-years approaching.

"Come on, you lot," he said. "I think Professor Dumbledore'd like to 'ear somethin' 'bout this."

Chapter Text

Mundungus led the way out of the Room of Hidden Things, forcing Jing Li Yao to walk in front of him. Sherlock, Molly, John, and Soo Lin followed in the young men's wake, none of them speaking. Sherlock was still carrying Ravenclaw's diadem, which twinkled innocently at him whenever they passed a torch. His brain was buzzing with questions, particularly for Soo Lin, but he knew the time to ask them was not now.

Mundungus led the others through the quiet castle until they reached a stone gargoyle in an out-of-the-way corridor. "Fizzing Whizbee," Mundungus said to it, and the gargoyle sprang aside, revealing a stone staircase spiraling upward into one of the castle's towers. Mundungus and Jing Li got on first, and the four third-years followed apprehensively. Higher and higher they climbed in tight circles, Sherlock fighting the dizziness, until the staircase ground to a halt. Mundungus tapped the griffin-shaped knocker on the wooden door before them, and for the first time, Sherlock and his friends walked into Professor Dumbledore's office. While no one was looking, Sherlock slipped the diadem into an inner pocket of his robes.

Even in his state of advanced nerves, Sherlock appreciated how lovely the room was. Circular and airy, the room was full of small tables with serenely puffing silver contraptions, and the walls were lined with dozens of portraits. Professor Dumbledore stood up from behind a mahogany desk and approached the small party. "Good evening, Mundungus," he said calmly, his bright blue eyes flickering briefly to Jing Li. "I see you have found the culprit behind these strange messages and attacks."

Sherlock gave a start. Dumbledore knew about the runic messages? He seemed to read Sherlock's mind, however, for he smiled and said, "Professor Wilkes informed me of the situation once Charles Lucas was attacked in the library. I do not believe any of you know this, but Mr. Fletcher here has been cooperating with the Aurors in quite a project. If you wish, Mundungus, you may explain to these four what they have stumbled upon."

"Right," said Mundungus. He waved his wand, and four plain wooden chairs appeared out of nowhere. Sherlock, Soo Lin, John, and Molly all sat, and Dumbledore returned behind his desk, as Mundungus began speaking. "See, you lot, I'd gotten meself in a spot of trouble my las' year at 'ogwarts," he said, keeping his wand pointed at Jing Li. "Tryin' to make a bit o' extra cash, I ran in with a bad lot. The Brotherhood of the Black Raven, they called 'emselves."

"A secret organization, specializing in the black-market trade of magical artifacts," said Dumbledore. "Many of these artifacts are incredibly rare treasures, and fetch handsome prices from private sellers. The Auror Office has had quite the time breaking this organization up, as it has many branches across Britain."

"Anyway," Mundungus continued, "I was part o' the branch 'ere at 'ogwarts. Not a real member, mind, just someone keepin' tabs on what was round the school. But when the Brotherhood started lookin' to sell somethin' priceless, somethin' that belongs in a museum, I didn't want nothin' more to do with it."

"Ravenclaw's diadem," said John quietly.

Mundungus nodded. "Thing was, it ain't exactly easy gettin' out o' somethin' like the Brotherhood. That's when I came to Dumbledore," he said, nodding at the headmaster, "an' he reckoned he could help me. I started workin' with the Aurors as a spy, helpin' them find the ring round 'ere. Their hidin' place was - "

"The Shrieking Shack," Sherlock supplied. "It was in one of the messages we found."

"Precisely," said Professor Dumbledore. "Once Mr. Fletcher informed the Auror Office, the Shack was raided and the members present put under arrest. The only one missing was the actual writer of the messages, and the attacker of both Professor Wilkes and Charles Lucas. I can only assume that you believed Professor Wilkes and Mr. Lucas to have knowledge of the diadem's whereabouts?" he asked Jing Li politely.

Jing Li scowled. "They were both runners for the Brotherhood," he said coldly. "Smuggled artifacts out of the castle. But they both deserted, and Wilkes is just lucky he didn't know anything."

"So, tonight, Professor Dumbledore set me to keep a watch in the castle, just in case," Mundungus said. "An' I was glad I'd been put in the seventh-floor corridor, 'cause when I saw 'im followin' you three in I knew he wasn't up to nothin' good."

Professor Dumbledore nodded. "Mundungus, if you would please inform the Auror Office that we have caught the final member of this branch of the organization," he said, pulling parchment from his desk. "You four," he added, "if you are unhurt, would best be off to your dormitories. Rest assured, your Houses will all receive a nice sum of points for the service you have offered." He smiled slightly before adding, "Off you go, now."

The four third-years left the office and separated to their dormitories. Soo Lin and John went up the twin marble staircases, leading to Gryffindor and Ravenclaw Towers. Sherlock turned toward the forest tapestry, eager for bed, but Molly plucked the sleeve of his robe.

"Soo Lin had something to do with that Brotherhood," she said quietly. "Why else would Jing Li have come looking for her?"

"Tonight isn't the night, Molly," Sherlock said wearily. As much as he burned to question Soo Lin, his eyes were itching with tiredness. "We'll see her soon, I expect."

Molly nodded, recognizing defeat, and pushed aside the tapestry hiding the entrance to the basement. Sherlock went through his own tapestry, back down to the Slytherin dungeon. It was only when he was safely in his dormitory, and had made sure no one was looking, that he pulled the diadem out from his robe pocket. Shining eerily green in the lake-water light, the delicate silver circlet seemed to have a strange magic of its own. Etched in tiny words across it was the motto of Ravenclaw House: Wit beyond measure is man's greatest treasure.

Carefully, Sherlock folded the diadem inside a spare set of robes in his trunk. He would decide what to do with it in the morning. He fell into bed without even bothering to undress and was asleep within moments.

Chapter Text

The next day, Sherlock gathered together Molly, John, and Soo Lin out in the grounds after breakfast. Spring truly had set in at Hogwarts now. As they left the castle, the four third-years could see bright patches of wildflowers growing at the edges of the Forbidden Forest. Distantly, they heard several loud, geese-like honks coming from the greenhouses. Molly smiled at this and said, "The honking daffodils are in their blooming phase."

Sherlock and John laughed, but Soo Lin only smiled. She was the first to sit down under their usual favorite tree, and Sherlock summoned his courage. Clearing his throat slightly, he said, "So they caught the message writer."

"You want to know why he came to me," Soo Lin said. It was not a question, and Sherlock did not reply. Beside him, John and Molly stiffened slightly. Soo Lin took his silence as assent: she sighed and said, "I was a part of the organization. The Brotherhood of the Black Raven." She pulled aside the neck of her robes and leaned forward. Feeling awkward, Sherlock looked: a tiny black raven, identical to the one on Jing Li's wrist, was tattooed onto her left shoulder.

Soo Lin let her robes drop and leaned back against the tree. "What Professor Dumbledore and Mundungus Fletcher said last night was true," she continued. "The Brotherhood specializes in finding magical artifacts and selling them privately for a huge profit. But the whole organization centers on finding one particular object."

"Ravenclaw's diadem," said Sherlock.

Soo Lin nodded. "My family initially refused to help the Brotherhood," she said. "But we had no choice. One of my uncles disappeared mysteriously when my father refused them. All the Aurors ever found of him was a finger, with a raven carved into it." Molly shuddered, John looked sickened, and Sherlock felt a little queasy himself.

"Last year my parents walked out like Mundungus did, and took me with them. They'd finally had enough," Soo Lin said sadly. "But my brother stayed. The ringleader of our branch, the Black Raven General, had promised to split the profits of the diadem with him. My parents had severed all contact with the Brotherhood, and my brother, but he knew I was still at Hogwarts. He thought I might have information."

The truth hit Sherlock with the force of a stampeding troll. "Then that man - Jing Li Yao - "

"My older brother," Soo Lin said. Her eyes seemed oddly bright, and she turned her face away from the other three. When she spoke again, she sounded as if she had a bad head cold. "He threatened me; you saw his signature on my bed. So I hid in the Room of Hidden Things, and hoped he wouldn't find me."

"But you didn't know anything about the diadem?" Sherlock said.

"No."

A long silence greeted Soo Lin's story. Molly put a hand on her friend's shoulder as she dried her eyes. Finally Soo Lin spoke again. "I just hope no one's able to find it again. They shouldn't; Jing Li is in Azkaban now."

In that moment, Sherlock came to a decision. "We'll make sure no one does find it," he said. "Come with me." He led the way back into the castle, his friends hurrying in his wake. He led the way down into the dungeon, through the Slytherin common room, to his dormitory. Pushing aside robes and spellbooks, he found the parcel he'd wrapped last night. Without speaking, he and the others went back up to the seventh-floor corridor. Sherlock closed his eyes, thinking hard: I need a place to hide something.

The room sprang into being, just as he'd figured it would. Once again the four third-years were back inside the cathedral-like space, filled to the brim with centuries' worth of secrets. Sherlock wandered through the alleys bordered with junk until he and his friends reached the back of the room. Turning to them, he unwrapped the robes, revealing the glittering diadem.

At its reveal, both Molly and Soo Lin gasped. "You still had it?" spluttered John.

"Yes," Sherlock said.

"But - but we should tell someone we found it!" said Soo Lin. As a Ravenclaw, she perhaps had the best understanding of the diadem's importance. Her dark eyes were wide with wonder as she gazed at the delicate circlet, its sapphires and diamonds sparkling in the light coming through a window. "That's been lost for centuries, everyone thought it vanished along with Rowena Ravenclaw herself!"

"No," Sherlock said. "It's an object from one of Hogwarts' founders. It belongs to Hogwarts, and it should stay here." Turning away from the other three, he put it inside a stack of objects, near an acid-blistered wooden cabinet and a bust of an ugly old warlock. That done, he turned back to the others. "Come on, let's go."

None of them argued with Sherlock. He, John, Molly, and Soo Lin weaved back through the piles of hidden objects, the home to which Ravenclaw's diadem had been returned. As they left the Room of Hidden Things, they watched as the wooden door sank out of sight and became stone once more. Without looking back, Sherlock led the way along the corridor, heading once more for the sunlit Hogwarts grounds.

The End