There was something that Mycroft Holmes could not work out.
He detested this.
He first noticed the pattern after a year, when the third person he had identified as a high-ranking actor within Moriarty's criminal network happened to come to a violent and unsolved end. One was chance; criminals died at the hands of other criminals with alarming frequency. Two was coincidence; it was logical that other criminal networks would be consolidating in the face of a collapse of Moriarty's. But three, three was a pattern. Three suggested that there was something going on. Three unsolvable murders meant something.
He kept a file, a physical one; he liked physical files, sheets of 120 GSM A4 against his fingers, the figural solidity of facts. Into this file, he dropped a murder in Rotterdam, the surprising arrest of a weapons dealer on a charge of the equivalent of death by dangerous driving in Nebraska, the assassination of three high-ranking members of Amal in the Bekaa, a string of explosions at human trafficking centers in Mali, a body fished from a canal in Venice. Every two months or so, he would pull out the file, consider its recent additions, try to see if he could find the pattern. But he couldn't. It didn't run parallel to his investigation--he often identified individuals only to find they'd been eliminated weeks before, and twice now he'd received notice of their murders or arrests on unrelated charges from agents who had been following them for months--therefore, it wasn't a leak. There was no counter-effort to rebuild the organization, which was growing ever more scattered and dissolute, so it wasn't a power grab by an individual trying to reconstruct it. It was just the random yet apparently methodical execution of every member of the network and the destruction of the totality of their assets. There was no answer he could come up with that fit the available evidence.
Except there was one. Two, possibly, but one of them he could prove was false: John Watson had been abroad only once, for his honeymoon, in the five years since Sherlock's death, and the timing was incompatible with any of the incidents. It didn't fit the available evidence anyway, because John Watson was a soldier, not an executioner. He followed the laws of war, none of which would permit castrating a sniper and leaving him to bleed to death in a back alley in Singapore.
So that was one. The other was equally impossible. He knew this. He was certain.
He was becoming less certain.
In any case, Moriarty's network was no longer a central concern of his portfolio--it had been too well demolished, both by Mycroft and the unknown actor. Among his colleagues, his continued interest was viewed as an eccentricity. They thought it sentiment. He found that pleasantly ironic and did not bother to change their impression.
He settled down at his desk and brought up the footage he had requested. A third death by a target who was being surveilled, and, this time, they had been lucky; his agent knew the target's whereabouts until ninety-seven minutes before her body had been discovered, still warm, hanging from a bridge in Buenos Aires. (It hadn't been physical surveillance--digital only--so the agent still had a job. One of the previous agents did not.) He had four different CCTV angles on the location, and a full hour's worth of tape before and after. He poured himself a cup of tea from the barely-warm pot sitting next to him on the desk, and hit play.
He ran the four threads simultaneously; if he did not see anything meaningful in them like this, he'd likely do them one at a time, but he might at least be able to narrow his window. At one hundred twelve minutes to body-discovery, the target appeared. She made her way to a bench and took a seat; the bench was obscured from one of the angles, but Mycroft left that open, in case she crossed past it again. His eyes were flickering between the three remaining images, and he saw her stand, and begin to walk away. There--a figure following her. It was obscured in the remaining footage, but it was unmistakably following her, hands tucked in the pockets of its jeans, chin down.
He watched the rest, but neither the target nor her apparent assassin reappeared. So he went back to the moment they disappeared from frame, and began running it backward, one thread at a time, watching for a clear view of the other player. It was hard to get a good shot of him (the program informed him the figure was six feet tall, and its torso was not noticeably female, plus the strangulations suggested upper body strength, if there was a single actor for all of the deaths, so he assumed it was a man); he seemed to know where the cameras were, and was careful to avoid the street lights. Mycroft began to worry that he'd need to get all possible surveillance footage on the target in order to identify the figure--and that he'd need to outsource it to someone else, he simply couldn't afford the time. But then--
He paused the footage. There. The figure was illuminated from behind, chin turned to the side, and that profile--
He knew that profile.
He kept that one frozen, switched to another one, ran the images as quickly as he could process. There, this image, the motion of the arm as it held a cigarette to his mouth. The shape of the mouth holding the cigarette, the angle of the wrist.
He kept working. Never a full image of the face, never a proper look at him, but the angle of a cheekbone from above as he walked after the target, the shape of the hand as it threw the cigarette butt, the curve of a shoulder. He froze the video, took screenshots, lined them all up in front of him.
He stared at them for a long moment. Then he touched his intercom. "Ms. Devetzi? May I have your assistance for a moment?"
Anthea came quickly; he realized she must have been able to hear that he was not quite himself. "Mr. Holmes? Is there a problem?"
He tried to find a way to explain what he needed. "I was looking at the surveillance footage I requested. I need--" He considered. "I need you to look at something."
So he showed her, first, the footage of the target leaving, and the figure following her. And then he brought up, one by one, each of the images he'd captured of the man who followed her, and left them open on the screen.
She stood next to him, and leaned in to examine the images. At the fifth picture he opened, the one of the profile, the one he'd saved for last, she gasped. "That arsehole," she said. She startled to hear herself say it, as if it had been involuntary, and glanced over at him.
He began to laugh, quietly. And then he realized that it wasn't precisely laughing he was doing, or it wasn't going to be in a moment, and he pressed his hand over his mouth and closed his eyes, trying to hold it in. Her hand came down on his shoulder, and he found himself leaning into her side, eyes closed, trying to get ahold of himself. When he opened his eyes, she was smiling at the screen, and glanced down at him, the faint lines at the side of her eyes radiating everything he didn't know how to express. She nodded, slightly.
He pulled away from her, and sat back up, but appreciated that her hand remained rock-solid on his shoulder. "Well, Ms. Devetzi," he said, putting his hands on his desk so they would stop shaking. "It appears we have a new target for surveillance."
"Yes, sir," she said, squeezing his shoulder.
When she left, he began the process of identifying the individual in the photograph with an investigation number, and authorizing an analyst downstairs to begin the process of digital tracking. He set the process in motion, and throughout, he felt something light and sharp burning through his brain, making it nearly impossible to function.
Because it had been impossible, but he was right, in the end. He had known who it was running just ahead of him, all along.
Sherlock was alive.