St Bartholomew's Teaching Hospital, 2009

Sherlock lifted the dropper and held it, poised over a Petrie dish filled with his latest experiment. Molly Hooper, the pathologist from the mortuary downstairs, had just sent him a text confirming his theories on his latest case; the man had been beaten before he was killed, which made the Yard's suspect's alibi perfectly solid; eyewitnesses had placed him three blocks away five minutes before the victim was murdered.

Like a fox in a meadow, he'd transitioned immediately onto the next distraction. They were all pressing until they were solved, but at the conclusion he darted away like a frightened butterfly to the next place of safety and interest. His mind rebelled at stagnation.

He heard voices in the corridor outside the lab and looked up; this lab was on the top floor and hardly used by anyone except the staff, and even them only on occasion. That was why he used it so often, because technically he wasn't staff. He was only allowed in here because Molly had taken pity on him, once upon a time. But the voices did not belong to the mousey, shy woman. They were men's voices, one he recognised, one he didn't.

A brisk, cursory knock announced them before the two men entered; Mike Stamford, a lecturer to the third-year oncology specialists, and another man, who entered the room with a wry, old-man's comment of, "It's a bit different from my day."

Sherlock smiled tightly and looked up; the second man was short and stocky, his face comfortable in the haggard look acquired by men who have been through extreme circumstances, a plastic standard-issue cane swinging idly in one hand. Right leg. Psychosomatic. Army doctor. Abroad – Afghanistan, maybe. Or Iraq. No way to tell. Pension isn't enough to sustain his living style – Stamford's brought him here as a potential flatmate. Bless him, he thought I was serious. He made as if to look away, but then something – something in the way the newcomer moved, held himself, gazed around the laboratory with steely, determined hazel eyes – twigged in his memory.

"You've no idea," Mike replied airily. Sherlock, recovering himself from the search for the memory that seemed to be right on the tip of his tongue, busied himself hastily in the experiment, picking up the dropper again.

He wanted to find out more about the man, needed more information to pursue the recollections hiding at the edges of his subconscious, like chasing someone's heels around the corners of a labyrinth. More information. That reminds me.

"Mike, can I borrow your phone?" he asked quickly, as usual skipping pleasantries. Perhaps if he behaved as he usually did, the man would venture the information on his own. "There's no signal on mine."

Mike Stamford frowned, and Sherlock could feel it boring into the top of his head as he refused to look up. "What's wrong with the landline?"

Sherlock shrugged. "I prefer to text."

"Sorry," Stamford shrugged innocuously. "It's in my coat." It wasn't, Sherlock could tell. That was the problem with Stamford: he could be quite stubborn, and entirely the type to cut off his nose to spite his face, or whatever the expression was. Sherlock frowned slightly at his Petrie dish.

"Oh – here," cut in a firm, solid voice that again pulled on the tinkly bell of memory at the back of Sherlock's head. "Use mine."

Sherlock looked up at the man, rummaging in the back pocket of his jeans – cheap but sturdy, limited income but not willing to skimp on quality: sensible – and then at Stamford, fishing for an introduction. A name. Just give me a name, and I'll remember. "Oh," he said, the surprise not entirely false. "Thank you."

"This is an old friend of mine, John Watson," Stamford introduced finally as Sherlock started to weave his way and accept the phone from the doctor. Smartphone. Second-hand. Inscription on the back – Harry Watson. Brother? Alcoholic. Married, separated. Not liked by John – John. John Watson. I still don't remember – why can't I remember him? It must have been a long time ago.

Sherlock took the phone and flipped it open, locating the messaging application without difficulty. If brother has green ladder, arrest brother. SH. As he tapped out his message to the Detective Inspector on their case, he cast a quick glance at John Watson. "Afghanistan or Iraq?" he asked. Not that it matters. I haven't been to an army base in either, so that isn't it.

John Watson's head tipped to the side and Sherlock felt like screaming with frustration. Why couldn't he remember, when with every little thing he did this man pulled the strings to make his brain dance? "I'm sorry?"

"Which was it," Sherlock repeated patiently, "Afghanistan or Iraq?"

He could feel Stamford smirking as John looked down at his leg. "Afghanistan… sorry, how did you –"

The door opened and Sherlock snapped away to greet Molly as she brought him coffee, but his brain wasn't in it; John Watson was in the corner of his eye, stoic and firm but broken-looking, and he knew without remembering anything that the doctor had not been broken when they had met before. Because they had met before, he knew that surer than he knew anything, and he was Sherlock Holmes.

In that moment, when his mouth fired off something that probably wasn't very nice to the young pathologist and turned away to take a sip of the frankly insipid coffee, he made up his mind. For whatever reason, he couldn't remember John Watson, and the fact that he wanted to so badly had to mean that he'd been important. Once upon a time, John Watson – whoever he had been – had been important to him.

"How do you feel about the violin?"

The words were out of his mouth before he could even think about stopping them. Never mind that he hadn't been serious when he'd challenged Stamford to find him a flatmate, never mind that he'd never had one or wanted someone so close so often before. John Watson looked around as though checking Sherlock wasn't speaking to someone else. "Sorry, what?

Sherlock took a deep breath. Here goes. If he doesn't remember me by the end of this, I'll… be extremely puzzled. "I play the violin when I'm thinking. Sometimes I don't talk for days on end. Would that bother you? Potential flatmates should know the worst about each other."

He gave a crude approximation of a bright smile, feigning indifference. John Watson looked taken aback, and he felt his smile slide into something real at the knowledge that he'd surprised and even impressed the bold army doctor. John Watson looked accusingly over at Stamford. "You told him about me."

Stamford was looking pathetically smug. Sherlock felt another flicker of irritation. He couldn't be given the credit for this – whatever this was, and he couldn't shake the feeling that it was one of the most incredible coincidences that fate could ever throw his way. "Not a word," the lecturer said smugly.

"Then who said anything about flatmates?" John Watson asked; Sherlock could hear his own irritation reflected in the army doctor's warm voice. He smirked.

"I did," he replied brightly, half-turning back to John Watson as he shrugged his coat on as though this, the invitation, the proposition, had been his plan all along. "I told Mike this morning that I must be a difficult man to find a flatmate for, now here he is, just after lunch with an old friend clearly just returned from military service in Afghanistan. Wasn't a difficult leap." The difficult leap, he thought wryly to himself, was what came afterwards, ignoring the doctor's question about Afghanistan: "I've got my eye on a little place in central London; together we ought to be able to afford it. We'll meet there tomorrow, say, seven o'clock?" He tossed the doctor another smile, wrapping his scarf around his neck, preparing for a hasty exit so he could drop the air of complete composure. "Sorry, I've got to dash – I think I left my riding crop in the mortuary."

He was almost at the door, struggling to breathe – he hadn't felt this constricted, claustrophobic, desperate since he'd first met Julien in high school – when John Watson called him back. He sounded annoyed. "Is that it?" he said loudly. Sherlock stopped, forcing himself to breathe normally. Julien. Why was that sticking in his mind?

"Is that what?"

John Watson snorted incredulously. Sherlock had the distinct impression he'd missed something important, again. "We've only just met, and we're going to go and look at a flat?"

Sherlock shrugged. He needed to get out, to think about how his old university friend was related to this wounded army doctor. "Problem?"

Said army doctor exchanged a disbelieving glance with Stamford. "We don't know a thing about each other! I don't know where we're meeting. I don't even know your name."

He blinked a few times. He was so nervous that it started pouring out of his mouth, though he could feel his face stay firmly in place; Stamford would think he was just showing off, no break from the norm. I know you're an army doctor who's recently been invalided home from Afghanistan. I know you've got a brother who's worried about you, but you won't go to him for help because you don't approve of him; possibly because he's an alcoholic, but more likely because he's just walked out on his wife. And I know that your therapist thinks your limp's psychosomatic – quite correctly, I'm afraid. That's enough to be getting on with, don't you think? It's not –

He realised he was talking out loud and quickly shut his mouth and successfully kept the last sentence in his head. It's not enough for me. There's more, I know there is. You know it too, I can see it in your eyes. What happened between us, John Watson?

He forced a smile, the claustrophobia constricting his chest until he was sure he must be deathly pale – how did he not look like he was about to collapse? – and swept out of the room. This time, John Watson didn't say anything. Sherlock allowed himself the smirk as he reached the door, and then turned back, remembering the rest of the doctor's complaint.

"The name is Sherlock Holmes, and the address is 221B Baker Street." In keeping with his usual brevity, despite his hitherto dormant nerves screaming at him, he clicked out an insouciant wink and waved at Stamford on his way out. "Afternoon!"

Outside, once he'd swept around the corner out of view from the laboratory, he leant against the wall and breathed deeply. John Watson. John Watson. Thinking of Julien had stirred something in his memory – had he met John Watson around the same time, during university or the end of high-school? He closed his eyes, willing himself to remember. He remembered disappointment, and restlessness, and a ride on the tube back to his French lover's arms.

John. Oh, God, John… how could I have forgotten you?

Suddenly every moment floods back, the smell of chlorine in his nostrils, the wall of the hospital growing sharp and textured into his memory.

Seventh form. 1992.