There was not much of the flat to search, as it happened. Whether he was his own father, his present self, his past self or some parallel version of himself, John Watson was still neat and tidy. Under the coffee table, hidden by a tablecloth that both of them had recognised as too out of character to be meant as a decoration, was a cardboard box full of various items: The Browning, a leather-bound Bible, and discharge papers from the Royal Navy. John had been invalided out on October 13, 1982.

"Standard discharge papers," John reported, looking them over. "Apart from the dates, they haven't changed very much in a few decades." But he still sounded troubled. "And they're in my name. Dad's middle name was—is—James."

"I know."

"Will you stop doing that?"

Sherlock opened his mouth to protest, then decided to shut it again.

"Anyway, his rank was Lieutenant Commander, and he didn't have any medical training," John went on matter-of-factly. "According to this, mine's Surgeon Lieutenant, and I was an MO on the HMS Ardent."

"What happened to you?"

"Doesn't say. I doubt anything good, because the Ardent was sunk after being bombed by Argentine aircraft. I can't remember exactly when, but I'm pretty sure it went down early in the conflict. There would have been, say, at least three or four months between the sinking and when I was formally served papers." His hand crept under the collar of his shirt, fingers moving toward his left shoulder.

"Scar?"

"Still there."

"Shame."

John glanced up. For once, he wasn't sure if Sherlock was being sarcastic or not. After a long and puzzled pause, he said, "Look, if we just went out to where my family were living in 1983 and checked—"

"—We would break the time and space continuum. So don't even think about it."

"I'm pretty sure it's broken already, Sherlock. Or at least, there's a good-sized dent in it."

But Sherlock did not respond to this. He was pacing around the room, restless, looking out the window at nothing, checking the skirting boards for nothing, covering his nose and mouth with his hands every now and again, tugging at his hair, giving the wall between the living area and the bedroom a frustrated slap that was two degrees away from a punch. After a few minutes of this, John checked his watch.

"One hour, fourteen minutes," he announced.

"Hmm?"

"You're missing your phone, aren't you? That's how long it took you to start going crazy without it. An hour and fourteen minutes."

"Oh, shut up," Sherlock snapped. "What do you think I want it for, to play FreeCell? I need it. It's important."

"It's useless to you anyway," John said. "Mobile towers don't exist, and neither does the internet." He got up. "Come on, we haven't finished looking."

"Oh, you seem to have gotten over yourself!"

John, to his own surprise, had. The conflicting data around him was too interesting for him to sit and worry about breaking the time and space continuum. He went into the bedroom and Sherlock, sulking, followed.

The bedroom was bigger than his at Baker Street, and better kitted out: a double bed in the centre of the room with a sturdy headboard of dark wood and a nondescript blue-grey duvet that, he thought, was more like something he'd have actually chosen for himself than anything he'd seen in the flat so far. Other than this, there was a set of bedside tables that didn't match the bed, being in a lighter walnut-coloured wood, and surmounted by a pair of flimsy lamps with cheap blue shades. The one on the far side of the room was rarely used, judging from the coating of dust on it. The other was obviously on his preferred side of the bed; along with it was a clunky grey phone. In the corner between them sat an old-fashioned Teledex. John sat down on the bed and picked it up with a comforting flash of recognition. He hadn't seen one of these in years. Sherlock, meanwhile, had gone to the wardrobe on the opposite wall and half-disappeared inside it, apparently pulling things out at random.

John ignored him. He opened the Teledex, starting at A, and worked his way through his (apparent) contacts. Almost all were Bristol numbers, and none struck him as familiar. There was one number listed under Surgery and, tucked in next to it, a piece of scrap paper listing five ten-hour timeslots, one each day of the week, except for Monday and Friday.

"What day is it again?" he asked vaguely, reading them through.

"Friday."

"Looks like I've got work tomorrow. I knew I couldn't be a full-time FME—they're normally on a roster, one or two days a fortnight, or else they're on call for a particular case." John got up and crouched down beside the bed to look under it, finding what he expected: a thick phone book. He yanked it out and sat down again, flicking through it to find the address of the surgery he apparently worked at.

"You look at that, then." Sherlock dumped something on the floor of the wardrobe with a heavy thunk and stood up, reaching for the door handle. "I'll make coffee."

John might have normally expressed more surprise at this declaration, but it had been a strange day already; and anyhow, he was busy looking through the listings for medical practices in the area. His only reply was a vague murmur.

By the time Sherlock had brought coffee in for both of them, John was writing an address down on a notepad he'd found next to the phone. "Pembroke Road," he said, reaching out for the cup Sherlock handed to him. "Wherever that is. I suppose I can just give a cab driver the address. Oh—yeah, Lestrade's info's in here, too. He's got a flat in Broad Street, apparently."

Sherlock took the Teledex, figuring out how to work it and going through the listings again. There weren't many, but one was very interesting. Eventually, he said, "So. 'Donna'."

John looked irritated. "You know I don't know who that is."

"No," Sherlock agreed, upbeat. "But all of these entries are in your handwriting, and I note you've listed no surname or address for this woman."

"So?"

"So you know her very well, and there's every likelihood that she lives in this building."

"Oh, God, that's the last thing I need," John said, but his interest had been piqued, and clearly, he wasn't thinking too carefully about one Sarah Sawyer. He reached out for his coffee and sipped it again, lost in thought.

"There's one thing you haven't mentioned," Sherlock said, "if you even noticed it, which is doubtful."

"What?"

"Nothing in this flat indicates you know me at all. You don't even have my phone number or address near the phone."

"Maybe I know it by heart."

"Do you know it by heart?"

"No," John had to confess. "But be fair. I don't know Harry's or Mike's or Greg's off by heart either. So what's all that mean?"

"I'm here," Sherlock said, "so I clearly exist. But why is there no evidence of my existence? The police officers at the scene yesterday called to you by name. They gave no indication at all they'd even seen I was there. I am not easy to overlook."

"I believe you." John took another sip of his coffee. "Jesus," he muttered. "I didn't realise how terrible instant coffee was in 1983."

"For God's sake, I've already told you—"

"Sherlock, I understand the idea of time travel better than I understand the idea of parallel dimensions, so do you think you could just let me imagine it's really, truly 1983?"

Sherlock exhaled. "All right," he said. "And that's another thing. I need your help."

"Really? Could I get that in writing?"

"John."

"All right, fine, you need my help. About what, exactly?"

"Let's…" Sherlock took another breath, as if he were about to say something that pained him. "Let us assume, for the sake of argument, that we are in a standard time-travel dimension. This is a common scenario found in science fiction films and literature, yes?"

"Yeah."

"What happens?"

It was a moment before John understood what he was being asked. Sherlock was, as they'd established only days before, spectacularly ignorant about some things, and that included most novels, films, plays and television shows. John racked his brain for all the information on pop culture time travel available to him. Back to the Future… Doctor Who… Bill and Ted's Excellent Adventure…

"To… right a wrong, usually," he finally said. "You know, or make sure something important happens, because if it doesn't, the future can't happen. But then that leads to the Grandfather Paradox..."

"Hmm?"

"Well, say you're sent back in time to kill your own grandfather when he was a baby. You can't, because if you did, you wouldn't exist to be sent back in time to do it…" John set down the coffee cup on the bedside table, judging the distance badly and nearly missing it altogether. Then his hand went to his temple. "Sorry," he said, a little thickly. "I don't know what…"

"I do," Sherlock said, unconcerned. He gave John's shoulder a light shove and he collapsed sprawling onto the mattress, slack-limbed. "Pleasant dreams." He yanked the duvet out from the mattress and threw it over him. Whatever John's skills as a doctor, he hadn't recognised the taste of Valium in his coffee.

Sherlock moved quietly around the room for a minute or two, putting various items back in the wardrobe and in a very private denial that he was monitoring John's breathing. Once he was sure he was properly under but not likely to vomit or choke, he pocketed a dozen Valium pills and put John's medical case back from where he'd pulled it from the top shelf of the wardrobe. John hadn't seen it yet, and had no idea of the amount of restricted drugs that were casually sitting inside it. 1983 was, it seemed, a very medically irresponsible year, but that suited Sherlock's purposes just fine.

Sherlock had no car, no money and no familiarity with the local transport system, but he did have a basic understanding of the geography of Bristol, so he made his way to Broad Street on foot. It was now early evening, and as he made his way through the smoke-scented streets, the street lamps came on and various businesses were pulling down their shutters and locking up for the day. He found a newspaper stand on the high street that was still open and saw, on the front page, a school portrait of a gap-toothed, red-haired boy of about fourteen and the headline Where is Derek? But he had no money to buy a copy, and standing there reading an unbought newspaper was going to draw attention to himself. Fishing around in his pocket, he found and lit a cigarette—he'd taken it from John's packet, being confident John wouldn't mind if he even noticed—and walked on, thinking hard.

That he and John were somehow in the same place with Lestrade—Lestrade, only thirty years younger, according to John—could not possibly be a coincidence.

The flat listed as Lestrade's was above a little shop that sold cameras and developed film, and was reached by a back entrance that had no security door and was not, it seemed, even locked after dark. The stairwell was lit with a greenish fluorescent tinge. Sherlock climbed the stairs to the third floor almost soundlessly, thought stealth was not needed: he could hear loud music even from the ground floor, a fast-paced bass beat overlaid with jangly rhythm guitars and a strangled male vocal. When he reached the landing, he found a reinforced security door with a pale yellow light shining out from underneath it and music pulsing from behind it. He knocked and waited for the sudden dip in volume and the expected, characteristic "Hang on!". Then there was a beleaguered sigh and a series of shuffles until Lestrade slid the bolt across and opened the door, peering out as his eyes adjusted to the shifting light.

Sherlock had seen, as had most of Scotland Yard, what Lestrade had looked like at nineteen: there was a framed photo on his desk of him posing between a middle-aged couple, his parents, on the day he'd first put on a uniform. But he'd been dressed up and on his best behaviour that day. Now he was wearing a grubby white t-shirt, a pair of stonewash jeans, no shoes, and had a spliff in his mouth.

"Who the hell are you?" was his easygoing greeting. He pulled the spliff from his lip and turned his head to avoid blowing smoke in his visitor's face.

Why don't you know me? Sherlock wanted to shout at him. You know John! He'd have admitted outright to how petulant and jealous this sounded if it would only net him an honest answer.

"Sherlock Holmes," was all he said, holding his hand out to shake.

Lestrade, embarrassed but polite, moved the spliff from his right hand to his left and obliged. "Okay," he said, as if agreeing that if nothing else, this was the truth; nobody would be likely to make up a name like Sherlock Holmes. "I'm none the wiser, though."

"And you never will be," Sherlock said, in a low enough tone that Lestrade did not react. "I'm… working for the police," he finally said in a louder voice. "I'm a friend of John Watson." The word friend sounded strange in his mouth, and he almost repeated it to see how he liked a second taste of it.

"Oh." Lestrade scratched the back of his head. "Is he OK? He looked like sixteen shades of shit this afternoon."

"He'll recover," Sherlock said, deciding not to comment on this colourful turn of phrase. "I'm not here about John. I'm here about your latest case."

"Sorry?"

"The police found a body this afternoon. It's missed the evening papers, but it will be front-page news in the morning ones. Which means we don't have much of a head start—"

"No, seriously, who are you?"

Sherlock rolled his eyes. Dense as ever. He could, of course, pull out a series of deductions that were mainly deductions and some actual memories of Lestrade's background, his family, his personality, his interests. On the other hand, he could just… "I'm a consulting detective for the Metropolitan Police," he said witheringly. "And I'm currently being assaulted with the smoke from what is clearly not a cigarette. Hardly honourable behaviour for a sworn officer, now, is it?"

At this, Lestrade gave in and let Sherlock into the flat. If anything, it was smaller and even dingier than John's; a bedsit, with a single bed at one end of the room and the world's smallest kitchenette at the other. Like John's flat, it smelled strongly of damp carpet and cigarettes. Unlike John's, it was chaotic, with various objects strewn all over the sofa and the floor: takeout containers, dishes, cassette tapes, ashtrays, records and clothes. There was a pair of y-fronts slung over the foot of the bed, which Sherlock instantly decided not to take any notice of. On the back of the bathroom door hung Lestrade's police uniform, immaculately cleaned and pressed, with not a stray speck of lint on it. His helmet sat, pride of place, on a book shelf near the TV that seemed to hold mostly cassette tapes and blue-covered police training manuals. Of particular interest was the far wall between the bed and what was obviously a bathroom door. On it was a large corkboard, covered with dozens of pinned photographs, letters and press cuttings.

"I'm not high or anything," Lestrade said, glancing toward the door a little nervously, as if contemplating making a break for it. "Just had a rough day, that's all…"

"I don't work for the drugs squad." Sherlock held his hand out for the spliff, took a puff and handed it back.

"Look, I don't know how you found me, but if you're on the murder squad at Scotland Yard and someone's told you this is my case, or even that I'm on the case, you've got it wrong. I'm just a bobby. I'm still on probation."

Sherlock pointed to the corkboard on the wall.

Lestrade followed Sherlock's gesture, scratching the back of his head again; a meek, deferential gesture that proclaimed Oh, shucks, I'm just a nobody from Kewstoke. His accent, too, was a lot broader than the one he would end up using as a Detective Inspector for the Metropolitan Police, vowels curling toward r's in a way they wouldn't after five years in London. "Well… doesn't hurt to have my own opinions," he mumbled, embarrassed. "I'm hoping to make detective and work for the CID one day. Maybe even Scotland Yard, if I can get there."

But Sherlock was not listening to Lestrade's career ambitions. He'd gone to the corkboard and was taking in its contents. On the lower left, Lestrade had pinned a copy of the same school portrait Sherlock had seen on the front page of the evening newspaper. Red hair, gappy teeth. The boy's eyes were white-lashed, and, though it was hard to tell from the photograph, probably a greyish green. Under the photo was a piece of paper where Lestrade had written in sharpie: Derek Metcalfe 08/04/1968 19/10/1982 (3)?

Sherlock said, "Talk me through these murders."