Harry wasn't sure quite why he was doing this. He just... he just wanted to know. If it wasn't for... everything. If he didn't look just like his father, if he wasn't in Gryffindor. If he was just... Harry.
Snape looked up from his paperwork, irritated. "Don't just stand there, Fredricks. Come in. What do you want?"
Harry shuffled into Snape's office. Fredricks was a Hufflepuff in the year above him, willing to lend his face to a little 'prank', since he would escape Hogwarts for the real world in a few months anyway.
The bribe from Fred and George may have helped.
"I've been working on modifying a spell, sir. I wondered if you would look over what I have so far."
Snape narrowed his eyes.
Harry's deception could fall apart at any time, but this was the crucial moment. Either Snape would believe that a barely-average Defense student could be practicing advanced spell work, or he would realise something was wrong and force Harry to reveal the truth.
"Have I missed an announcement that Professor Flitwick is no longer employed?"
"No, sir. It's a combat spell, so I thought, as our Defense instructor..."
"And has this work been supervised, Mr. Fredricks?"
"Well. That is. Er." Harry flushed. "No, sir. I always put up shield charms, though! And the house elves know where I am."
"Ten points from Hufflepuff for your reckless behavior."
Harry silently cursed himself. He should have come up with a better story. Fredricks was going to kill him.
Snape shuffled his papers to the side and leaned forward, chin resting on his folded hands. "What spell is it you believe yourself to have modified?"
Harry relaxed fractionally. That sounded like Snape believed his story, if not Fredricks' ability to back it up. "The Knockback Jinx, Flippendo. It knocks things sideways now, rather than straight back. I thought, in battle, the unpredictability..."
Snape's eyebrows crept up in mild surprise. "Not entirely useless, though certainly there are spells that perform that function without modification."
"But the point is for your opponents to not expect it," Harry defended. "Even if they realise what you've done, you can swap back to the normal jinx..."
He fully expected to be torn apart for daring to disagree. Detention at a minimum. Snape despised 'arrogance'.
Instead, the man looked pleased. "Correct, Mr. Fredricks." Snape stood, cloak billowing. "Follow me. I would have a demonstration before offering unearned congratulations."
Harry struggled not to let his mouth hang open. "Yes, sir."
Snape swept out of the room and down the hall, Harry trailing behind. He was fortunate Snape was walking ahead. Fredricks was quite a bit taller than Harry, and he kept tripping over his own feet.
They arrived at what Harry at first assumed was an empty classroom just a few turns away from Snape's office. But inside there were no desks. Instead, there were dummies lined up along the far wall, and low bookshelves along another. It looked like a smaller version of the Room of Requirements when they were using it for the DA, and Harry began to wonder whether the Slytherins had had their own version of the club. Except that there was no chance Snape would show a Hufflepuff to a secret Slytherin clubhouse, which meant this was probably Snape's private practice room.
"If I find out that you or your friends have begun using this room without supervision, you will wish you were given detentions."
A shiver went down Harry's spine. He had no doubt Snape would keep his word. "Of course, sir."
Snape stepped into the room and flicked his wand, bringing a dummy to the centre. He muttered another spell that made the dummy wobble for a moment. "The room is already shielded. This will be your target. It will not require at least half the force of a full Flippendo to move. A light breeze will be useless. Let us see just how badly you've mangled the spell."
Harry straightened his spine, indignant. He would show Snape mangled. He marched over to stand well away from the door and with hardly a moment's pause snapped his wand out and cast. "Flippendo!" The dummy shot sideways and smacked into the bookshelves.
Harry turned to glare at Snape.
"You plan to use that level of force on your opponents, Mr. Fredricks?" Snape drawled. He flicked his wand again, bringing the dummy back to the centre.
Harry didn't reply, too busy reigning in his temper. Of course he didn't want to hurt anyone too badly, but his opponents were going to be Death Eaters. It wasn't like he would have a choice.
"Well? Cast it again. As you intend to use it, this time. None of that ridiculous showboating."
Harry cast the spell again at Snape's behest. The dummy jerked to the side and spun, but didn't fall.
"Hardly combat worthy." Snape reset the dummy. "Again."
This time the dummy hardly moved, but fell with a clatter.
Snape hummed and righted it. "I see. How have you documented your modifications?"
Harry blinked at him. "Documented?"
"Yes, you dunderhead," Snape hissed. "The arthithmatic calculations. The test results."
That sounded more like Hermione's area. Not that Harry hadn't read some theory trying to figure out how to make the spell do what he wanted. Or, well, he had listened to Hermione's study-rants on the topic.
And the spell worked, so clearly whatever Snape was talking about wasn't really that important. The Prince didn't have any numbers next to his spells.
"I just pushed the magic differently. I didn't... write anything about it."
Snape pinched his nose. "I thought ten points was enough to account for your recklessness, but clearly not. You could have radically unbalanced the spell and blown yourself up!"
Harry scowled at that. "I'm not an idiot! I don't finish a spell that's about to break!"
"Very few wizards are skilled enough to catch every instance, Mr. Fredricks, and you are certainly not one of them."
"Well I did."
"And next time you won't, and you'll be far to dead to regret your arrogance."
"Then show me how you think I should do it!"
Snape flicked his wand harshly, conjuring a blackboard stretched between them. He took up the chalk and began rapidly sketching a network of lines, followed by a series of numbers next to each.
Harry didn't know much about arithmancy, but he realized he should be very, very impressed. Hermione spent ages hunched over her diagrams, muttering calculations to herself. And here Snape was scribbling it all down without hesitation.
"The basic Flippendo, Mr. Fredricks. Given your four years of study with Septima, I might have assumed you would be capable of reading it, but you have proven yourself especially short-sighted today."
"I can read it fine," Harry grit out, lying through his teeth. He had a basic understanding that the lines corresponded to forces, but how one went from magic to numbers, he hadn't a clue.
"Very well. Now, explain your modifications."
Harry took a moment to work out the most 'technical' way to explain what he'd done, and squinted at the diagram. He was pretty sure that line matched up to one of the first changes he'd made. He pointed at it. "I made that one get more power from, uh..." He chewed his lip. "This direction. But then that was going to just blow itself out - out, not up - so I pulled these two closer together - which depowered this one, I guess. Well, actually I tried just cutting that one out but then it wasn't actually Flippendo anymore, so yeah, just depowered it."
Snape was staring at Harry with a sort of horrified fascination, which Harry did his best to ignore, despite the colour creeping up the back of his neck. Curse Fredricks' pasty complexion.
"Anyway, that made it work, but it was pretty unpredictable, so I figured I had to balance it out and powered up this one, too, but then it was, erm... Goingtoexplode. So I used the extra power there to power up the other part, here, and then it worked."
"I'm going to have to speak to Septima about your marks," was all Snape said before turning back to the board. His chalk changed from white to pale blue as he began to rapidly change numbers. Occasionally he asked for Harry's input about the relative powers of various lines, though in much more technical terms, which Harry did his best to answer. He had no idea what 'atunement' or 'aspect' meant in arithmancy, but he figured most of Snape's assumptions about what was happening would be right, so he just kept agreeing.
Once Snape was satisfied that the diagram accurately reflected what Harry had made, his chalk changed colours again and he made a series of adjustments. He turned back to Harry. "That you haven't managed to kill yourself yet is a surprise. That you crafted a functioning spell is a miracle. Now, we will elevate what you've done from 'functioning' to 'elegant'."
He began to explain his changes, Harry nodding along. It wasn't completely unintelligible, though Harry would certainly be asking Hermione for help later.
"Now, cast again." Snape sent the blackboard sliding out of the way and stepped back to give Harry room.
He cast slowly, with only enough power to make the spell function. The dummy practically leapt to the side, doing a full flip before crashing to the ground.
"Much more efficient," Snape commented with satisfaction. "Excellent work, Mr. Fredricks."
Harry continued to stare at the dummy, eyes wide. He had hardly needed any power at all, and he could tell that the spell would work - wanted to work - the same way every time. "Thank... Thank you, Professor."
They tested the spell a few more times before Snape ended the session by copying down the diagram onto a piece of parchment for Harry to take and leading them back to his office.
"You'll go tomorrow to pester Flitwick for the paperwork to have your modifications credited," Snape instructed, ushering Harry into the room.
"Of course, sir. Thank you. Will, um. Should you be listed, too, since you did all the final changes?" Harry really didn't want to. If Snape was expecting his own name to be on the paperwork, that meant Harry would actually have to submit it. Which he obviously couldn't do, because he wasn't really Fredricks.
"Obviously. You'll list me as the supervising wizard. Don't look so aggrieved. As if those dunderheads at the Ministry would bother to gossip about a spell registrations."
Snape sat back at his desk and reordered his paperwork. After a few words, he looked back up. "Well? Be off!"
Harry barely refrained from scrambling away. He shut the door to Snape's office and took a few steps before leaning up against one of the cold stone walls of the dungeon. He wasn't sure how to feel. Part of him was nervous. Now he had to figure out how to avoid submitting the spell. Part of him was snarling with rage. Snape could act like that? But never toward him. Another part was unwillingly charmed. Snape had been incredibly helpful, and for once his accusation of recklessness wasn't unfounded.
It had actually been... Fun. Harry had imagined talking to the Prince about his spells hundreds of times. The Prince knew so much more than Harry, just like Snape, and he could imagine the other boy snarking about Harry's arithmancy deficiency. It was almost enough to put a smile on his face, except that then he would be putting his Prince in place of Snape, and that was just a comparison he really didn't want to make.
Harry shook his head and got moving. There was nothing he could do about any of it. Snape still hated him. The Prince was either dead or years away from Hogwarts. And he had to report back to Fredricks to prevent any future mishaps that would reveal their trick. And then this would never happen again.
His one and only chance to meet a kinder Severus Snape was over.