In his defence, he was so tired that first day that most of it didn't even register. In fact, he's pretty sure it first happened the day before that one, and he hadn't noticed over the slight buzzing noise in his ears and the distinct feeling that Sherlock's latest taxidermy experiment had gone wrong and the detective had accidentally stuffed his head with cotton wool.

You see, Sherlock has had extensive self-training and eons of practise at not sleeping. John, not so much. So the still-dapper-and-enthusiastic consultant is pacing like a man possessed in the sitting room of 221B when he first notices it.

"…So my first instinct was entirely with the police on that one, but then how could he possibly have hidden it? Nobody knew him around there, it's impossible to keep an entire racehorse hidden in suburbia when your neighbours are all rubbernecking you…"

John sits on his armchair by the fire and watches, feeling his eyelids strain downwards. He just needs fifteen minutes of sleep and he'll be good to go. But of course, every time he's just about to drift off Sherlock starts up again.

"…but why didn't the dogs notice? The stable-boys sleep right upstairs, the dogs can't have barked at all or they'd have woken up. And what's more – John, are you still with me?"

John grunts in assent. Sherlock nods. "Good. Because I think I'm onto something here. Straker's knife was covered in blood, but the man the police took in had no wounds of any kind on him, and that walking-stick thing wasn't sharp enough to cause the cut on Straker's leg. So how did the cut get there?"

He looks at John like he's waiting for the answer, so the army doctor coughs, sits up straighter, collects the last facts the detective laid in front of him, lines them up like a buffet-train, and fits them into the conclusion that Sherlock probably reached hours ago. "He could've done it himself after he got his head bashed in. Convulsions caused by the brain injury."

Sherlock practically beams. "Exactly. Which pretty much takes away the last piece of evidence in favour of the accused. So, Straker's wife tells him about the disturbance, he grabs the knife from the kitchen table and runs out to the stable –" Sherlock's deep voice cuts off suddenly and his eyes widen. "John, you saw that knife, right?" John grunts again; Sherlock had nearly severed his nose off with it when he waved it in his face. "What kind of knife would you say it was?"

"It was a cataract knife," he replies immediately, realising the point as he says it. "Which wouldn't have just been lying on the kitchen table," he finishes, nodding. Sherlock's nodding too, looking positively gleeful.

"So…" he prompts eagerly.

"So Straker took the horse out of the stable to sabotage it in the middle of the paddock where no-one would hear it. But then who killed him?"

But Sherlock's already on the move, whirling around in search of his phone, thrown aside in disgust earlier. "The horse did," he says distractedly. "Remember the match outside the stable? Straker lit it behind him so he could see the right spot to make the cut, and the horse panicked and kicked him." With a crow of delight, he dives onto the sofa and digs his phone out from where it had fallen between the cushions and rushes out. John watches the magnificent body disappear into the bedroom, still blinking and trying to sort through the cotton wool to find what just happened.

Somewhere amid the clouds his brain remembers the adjective it just used to describe Sherlock's arse.

Wait, what?

However, by this stage he's too exhausted to think about much other than the fact that Sherlock has just solved the case and that means he'll be free to sleep after another hour or so of gloating, so it sticks a metaphorical Post-it next to the thought and flags it for later.

Of course, the consulting detective drags him along to the Yard with him so that he can berate the new young Sergeant he's taken a shine to for his lack of imagination and smile smugly in Lestrade's face when he gets the call from Dartmoor to say the horse has been found exactly where Sherlock said it would be. The DI gives John a world-weary look that turns quickly into a worried one. "Are you all right, John?" he asks gently as Sherlock waltzes off.

John's ears are making that buzzing noise again, so he doesn't quite catch it. "Hmm?"

"When was the last time you slept?" Lestrade asks. John blinks a couple of times.

"Um. I don't remember. I'm okay, he'll be done gloating soon." As he says it, Sherlock finishes his high-functioning analysis of why Anderson's new glasses make him look like he's just been hit in the face with a cow pat and turns back to John.

"I think that about covers everything," he says briskly. "Shall we go, then?"

John frowns. "You haven't insulted Donovan yet," he reminds him. "You've praised Gregory, crushed Anderson and gloated at Lestrade, but you haven't insulted Donovan. That's usually your parting blow."

The aforementioned sergeant turns the corner – evidently she's been purposefully avoiding the scene because of the ritual. Sherlock notices her with eyes full of glee. "Ah, Donovan. As always, you've missed everything of importance."

And with that done, he grins at the doctor, his grey eyes dancing, looking utterly mischievous and utterly kissable.

That's when John collapses.

It's probably that the realisation of what he'd just said – only in his mind, thank goodness – added one last frantic thought loop that blew the fuse on his brain. But whatever it was, the added stress of having collapsed and being manhandled by Sherlock and Lestrade into a cab drives the original thought right out of his head, to be filed next to the earlier Freudian slip he's forgotten about.

Except that night, he dreams about Sherlock.

It's a nice dream. Usually the only ones he remembers are set in Afghanistan and he only remembers them because he gets shot and the phantom pains wake him up. But when he wakes up the next afternoon feeling fully refreshed and ready for anything, he suddenly remembers a scene that he's pretty sure – pretty sure – didn't happen when they got home last night.

Sherlock shuts the door behind them, still with that delicious smile in his eyes. "Well, that was easy," he comments, stripping scarf and coat and dumping them unceremoniously on the arm of the sofa. "I'm starving. Should have thought of that when we were by the Chinese place."

John shrugs. "There's stuff from yesterday in the fridge. I'll heat some up." He opens the fridge and peers inside, but there isn't time to observe the contents before the consulting detective's body is pressed flush against his back, long arms snaking around his waist, a largish, strong nose tickling the join between neck and shoulder. "Sherlock?"

"Mmn?"

"What are you doing?"

"An experiment."

John isn't sure why these words make him relax – he's only dreaming after all, sometimes things just happen – but they do. "Oh." He leans back into the detective's arms. "Okay." Sherlock lets a deep, contented noise rumble its way out of his chest and resonate with John's body until his knees are rendered useless and his whole body vibrates with longing.

And when he wakes up he sort of knows. The way everyone sort of knows, really. John sits up and lets his short legs dangle off the side of the bed and remembers the dream, and his body shivers and tingles at the thought of it, and he realises that yes, right, okay, he'd really rather like to get his positively gorgeous flatmate into his bed and keep him there for an indefinite period of time.

And not being one to shy away from a challenge, that's all fine, really. Because he'll get there, eventually. It's all a matter of bringing the detective around to the same opinion.

So right there and just like that, John Watson decides to seduce Sherlock Holmes.