A/N: This was originally intended to be totally gen, but somehow a bunch of UST invaded and now it's very definitely pre-slash. The direction Sherlock's dialogue took also sort of turned it into a prequel to Bear It Out to the Edge of Doom (and basically makes that one officially pre-slash), although both are independent and can be read individually. (Warning: Edge of Doom is a WIP that probably won't be updated for a few more weeks due to a thorny little plot issue I'm figuring out.)

"A hundred percent?"

John turned from the window. "Nobody could fake being such an annoying dick all the time." He watched Sherlock just long enough to see his friend's mouth twitch the faintest smile before turning back to the window.

A few seconds later, Sherlock pushed back from his laptop, and John could feel that familiar icy gaze boring into the side of his head. "For what it's worth, Lestrade doesn't really believe it either. He's just doing his job, Sherlock. Moriarty set it up well enough to fool Donovan and now he's got no choice but to follow up on it."

"No, he doesn't believe it. But he did have a moment of doubt. Just a flicker, but enough to make him feel guilty for doing his job." John heard Sherlock stand up and finally met his gaze. Sherlock continued as he came around the desk toward John. "But you really didn't, did you? If you'd had even that flicker, you'd be wracked with guilt over it. You know me far better than Lestrade does and care about me far more; you'd feel far guiltier about it. None of this has even made you wonder, has it?" He stopped mere inches away from John.

"No, no it hasn't." John shrugged, feeling a bit off balance. He'd expected the look in Sherlock's eyes to be one of the usual cold deduction, possibly a hint of excitement if he were trying to puzzle out John's motivations or train of thought. Instead, there was something John wasn't sure he'd ever seen before in those grey-green eyes - sadness. Perhaps, even in the face of evidence, Sherlock was having trouble believing that even John could trust him so much? Not for the first time, John's heart broke a little for this man who had always understood human bonds more through theory than practice. "I live with you, Sherlock. Day in and day out. You're an arsehole and you're infuriating, but you're not a fraud. You lie to me, yes, but only when you've got a good reason. Although -" he pointed a finger at Sherlock sternly, "having a good reason does not always make it a good idea, I'll thank you to remember." Sherlock rolled his eyes, and John was just thankful for a break from that doleful stare.

"In that spirit, I have a confession to make," Sherlock directed his quiet words somewhere in the vicinity of John's wrist.

"If you're about to tell me you are Moriarty, I'm just going to laugh."

Sherlock's mouth twisted in a lopsided, mirthless smile and his eyes met John's again. "No. But I did think you were."

John blinked rapidly as he tried to parse out what Sherlock had just said. "You what? You thought I - What? You thought I was Moriarty?"

"At the pool."

"Oh." John's face fell slack as he remembered stepping out wearing the explosive vest, repeating the words Moriarty spoke into his ear, taking great care to get every syllable correct while blinking out SOS like a military hostage.

Sherlock moved even farther into John's personal space, and John couldn't take his eyes off of him. The sadness was back. "For one brief, brief moment - seconds, really - I thought you were Moriarty. Or to be more precise, I thought that you, Doctor John Hamish Watson, had never existed. I doubted your very existence for a few seconds, thought you were an invention like Richard Brook. My blood ran cold at the idea; I was so frightened I didn't even notice at first that you were wearing a different coat than you'd left the flat in. Not because I feared I'd been tricked, but at the idea of not only losing you, but never having had you in the first place. That you really had been too good to be true. "

John's breathing hitched and he was suddenly very aware of how close their faces were. He could feel Sherlock's breath against his skin, and if Sherlock's expression had been telegraphing anything other than pain he might have started to get the wrong idea about where this conversation was going. It would be the wrong idea, he reminded himself; that could never be the right idea about Sherlock.

"I know how guilty you would feel for doubting me because I've felt that way ever since. I don't believe in regrets as a general rule, but that has been one of my greatest: letting my trust in you slip for just a few seconds, John. Thank you for not being as weak as I was."

"Sherlock," John was nearly whispering, "You'd known me for two months then, barely. It's been a year and a half now. I probably would have doubted you then, too. Not anymore, not after everything we've seen together. If the pool happened today, you wouldn't have any doubts, either." He reached up and laid a hand on Sherlock's arm, giving it a quick squeeze. It was supposed to be a gesture of support, but just a second too late John realized that it felt suspiciously like an invitation for Sherlock to close the remaining scant distance between them. Panic spiraled up through him, but he couldn't take his eyes away from Sherlock's.

Sherlock, for his part, palpably relaxed at John's words, but his gaze only grew in intensity. Now instead of sadness, though, it contained a steely determination. John could feel it radiating off of him. "No, John. I have no doubts about you whatsoever. Whatever happens from here on out, I need you to remember that. You are the one person on earth in whom I have complete trust."

Trapped by Sherlock's eyes, John couldn't answer. "Okay" seemed inadequate; "take me" seemed rather over the top and not even what John really meant at all, was it? He wasn't so sure anymore. Sherlock's eyes bored into his and he felt utterly unable to break the contact, to move away even the few centimeters that would be needed to slash through the tension building between them. He finally managed a fractional nod.

"No matter what. Remember that," Sherlock breathed, and his eyes flicked down to John's mouth and Oh God, for just one second it seemed that he really might lean in, just another inch was all it would take. John could feel that Sherlock's breathing was as shallow as his, his pupils starting to shift - but then his eyes were breaking away. Without moving his face away from John's, Sherlock cast his eyes to one side for just a few seconds and the spell was broken. John considered disappointment, but discarded it and settled on relief as an appropriate response. Sherlock finally moved back just a few inches as his eyes came back to John's. Those eyes were smiling now. "Thank you, John. For everything." He squeezed John's arm in a mirror of John's arm on his, and the touch reminded John that it was well past time for him to take his hand back.

And then Sherlock was whirling away from him, pacing briefly and muttering to himself before settling into his armchair in his usual thinking pose. Whatever had been charging the air between them had cleared away almost instantly, and John suddenly found himself unsure that it had actually been there in the first place. The past few minutes felt like a half-remembered dream; the kind that's crystal clear when you wake up but fogs over too soon and is just out of your grasp before you've reached the shower. John stared out the window again and tried to at least commit the words that had passed to memory if not the feelings surrounding them, until the sound of his mobile ringing distracted him. He crossed the room to pick it up; it was Lestrade.