It isn't as though Sherlock hadn't thought John was objectively attractive from the start. He is, in a rather unobtrusive way, and that had been noted along with his limp and his military service and the cut and colour of his hair. But Sherlock had been done with attempts at sex for a long time when they met, and certainly wasn't looking for anything in the way of that from his flatmate when he proposed they move in together, even after he discovered the man was moderately intelligent and a crack shot.

Still, Sherlock does find himself studying John, for more than just the usual data to tell him about a person and predict his actions. He's riveted by John's self-contained movements, his placid demeanour, apt to be broken at the most unexpected moments by a vicious and blinding righteous anger, and most of all his face.

That face. They are the same age, nearly, and while John hardly looks old, his face is so much more weathered and lined than Sherlock's. Sherlock's face is smooth and pale and angular, boyish, like a teenager who grew tall too fast and didn't put on enough weight or a sculpture in marble. John's, though still young in many ways, is crinkly and a bit worn and full of stories he doesn't tell, and some very dark things behind his smile. But it is also kind and cheerful and unfailingly open and Sherlock can't seem to stop thinking about it.

And all of that would be completely fine except at some point Sherlock notices that he can't seem to stop thinking about the rest of him either.

Blue eyes that can be any shade from a that of a thundercloud to slate to almost the colour of Sherlock's favourite dressing gown, and that delicious scar he's only caught a glimpse of that reminds him of a map of London organically grown on his flatmate's skin, a compact build on which hangs a small but powerful body…

He's not a stranger to lust, and has never had trouble dispatching such thoughts before. And of course, lust is all it is, because it couldn't possibly be anything else. It shouldn't be this hard to get over. But then again, he's never had the embodiment of his lust living in his home and sharing his bathroom before, either. It is, above all other things, maddeningly distracting.

John is lounging around the flat in his ghastly striped dressing gown, the terry cloth one he wraps around himself after a shower in lieu of a towel. He's reading the paper innocently and waiting for his hair to air-dry. It should be illegal, Sherlock thinks, gripping a blank microscope slide hard enough to break it. He sucks the blood from his finger vindictively and glowers at the back of John's head.

He shouldn't have to deal with this, it's been so long and all he wants is to be able to work in peace without having sex unintentionally dangled in front him, particularly by a happily straight man, and maybe a quick wank is the answer to get it out of his system, but given the state of things that feels a little too close to indulging so he grits his teeth…

Parading through the flat like that, all soft and warm and damp, pink from the bath, hair tousled, the scent of plain soap and the Inecto lotion John got into the habit of using in the desert and his spicily mellow aftershave trailing after him. It's obscene really, how is anyone expected to focus like this? Sitting around completely naked under his robe, not even wearing pants. Is this really acceptable behaviour for a flatmate? It seems vaguely lewd.

Sherlock tears his eyes away from John's head and goes back to his microscope.

"Anything on today?" John asks absently.

Sherlock growls irritably, not even interested in forming sentences.

"Fine, if that's how you want it, I'll check." John reaches for his laptop, robe falling away from his legs just a tad and revealing a well-contoured calf.

"Can't you get dressed first?" Sherlock snaps, his gaze fixed on the shapely leg again his will.

He's got freckles on his legs, and some small scars, and if he stays still maybe Sherlock can figure out which are from the war and which are from falling off his bicycle when he was nine, though they are all of equal importance in the running catalogue of facts about John from which nothing is ever deleted…

"Tetchy today, are we? Well, I figure I might as well see if we have any cases worth getting dressed for. Otherwise I might not even bother, it's not like I have plans." John grins. He's worked out that his state of undress is annoying Sherlock but seems to have come to completely the wrong conclusion as to why. Good.

"God in heaven," Sherlock intones despairingly.

"You're the one who likes to laze about wearing nothing but a sheet. A robe is practically street clothes in comparison."

John in a sheet, John in one of the sheets off Sherlock's bed, John in Sherlock's bed, John wearing nothing but…

Sherlock abandons the microscope, along with the comparison of algae types in different London park ponds. Concentration is clearly going to be impossible this morning. He glares pointedly at the laptop. "Well?"

"Oh fine." John goes through his inbox and makes a face. "There's something from Seb."

Seb, his old friend who was always and really nothing more than an enemy, even when they shared a need and a secret, but an enemy it's better to keep track of, even though Sherlock wouldn't mind it so terribly if Seb was quietly run over in the tube and ended up splattered across three stations…

"Is it interesting?"

"Maybe. Missing girls from the secretarial pool. Well, not missing, they keep quitting suddenly but it's becoming a pattern. He thinks they're being threatened or something. And he'll pay plenty as usual. Going to take it?"

Sherlock rolls his eyes. "No. Call me when they start turning up in the morgue."

He expects a reprimand from John for that, but he just chuckles. "Good."

Now Sherlock is interested. "Why good? You usually get frustrated when I turn down cases that might actually pay."

"Yeah, but I really hate that guy."

"Seb? You hate Seb? You barely know him." This is proving to be most enlightening. John does not typically make strong statements of dislike about people he doesn't know well. He's very even-keeled, liking and likeable in general. At least to a point, and then he gets very unlikeable indeed, which is far more fun as far as Sherlock is concerned. But that point usually involves someone trying to kill someone else. Sherlock tries to recall if Seb has done anything to John in the three times they've met and draws a blank.

"I don't need to know him. He's a git. And a bully. We don't need his money."

Sherlock cocks an eyebrow. "You're spot on there, but I'm surprised you were able to deduce so much after such brief interaction."

"Is that a compliment? But it doesn't take any deduction, the way he talks to you is more than enough to get my hackles up. Add to that the fact that you clearly despise him and that's all I need to know. Plus everything about him screams arsehole."

Sherlock gives a private little smile, pleased.

John doesn't like when people talk about Sherlock badly, John gets angry and does foolish things because of it, John's allowed to tease Sherlock and call him an idiot and a prat and worse because in John's mouth those words sound like…

He does hate Seb. Hates him with the cold, lasting hatred and ancient loathing of someone you've known seemingly forever and just can't get entirely out of your life, possibly because you know just a little too much about each other. He changes the topic. "Anything else?"

"Lost puppies and unfaithful spouses, I'm afraid. That clinches it – no work, it's a Sunday. Not getting dressed."

"John…"

"Sunday, Sherlock. Have you no respect for a lazy Sunday? Maybe I'll spend the whole thing starkers in front of the telly."

He knows John is baiting him, clearly, but Sherlock panics.

John naked on the sofa, his sofa, stretched out, every blonde hair on his body catching the afternoon light, soft in a pose of relaxation yet hard in just the right

John laughs at him, misunderstanding his expression again. "Oh, calm down. It's just nudity, you get used to it. But as it happens I don't actually fancy sitting around with my tackle out all day, so I am going to get dressed. After I finish the crossword."

Sherlock begins to recognize in himself strange behaviours that in anyone else he would ascribe to jealousy or sentiment. He decides handle this by ignoring his inexplicable desire to rid the world of John's endless stream of plain jane girlfriends, his constant use of John's things without even a decent excuse, and his persistent need to talk to John even when he is apparently not in the room, city, or even country. He supposes he could go back to talking to his skull when John is away, but he prefers to talk to John. Besides, he doesn't always notice when John is gone.

Using John's things is like using John, like getting to be him for a little while, like appropriating ownership over him just a tiny bit every time Sherlock drinks from his tea mug or steals a piece of clothing to use as a rag to mop up an experiment or sends an email from his phone, putting his name and fingerprints and DNA all over John's possessions…

None of these, of course, indicate anything about Sherlock's feelings, they are simply things that happen and Sherlock works better when they do, so reasons behind them don't matter. Any partner of his would do better to focus on cases than girls, the work was far more important. He would go through the things of anyone who lived with him, it only makes sense to know as much as possible about who you were living with. And sometimes using someone else's computer or phone is just more practical.

Assuming Sherlock can get his little lust problem squared away, there is nothing alarming about any of it.

One afternoon John walks in the door and heads straight for the kitchen, but stops abruptly as he passes Sherlock in the sitting room. "Is that my computer?" he demands, motioning to the laptop upon which Sherlock is typing rapidly. "Sherlock, we talked about this!"

"Closer," Sherlock says tersely, without looking up.

"I just changed the password again!"

"Yes, well, FUCKOFFSHERLOCKYOUTWAT, while colourful, is neither cryptographically challenging nor physiologically accurate."

How pleasing that John would use his name even in an attempt to keep him out, how lovely that it's all a game or else he would have picked a random string of numbers and letters that might actually baffle someone, Sherlock wonders what the new password will be, whatever it is it will be designed just for him…

John sighs. "Oh, suit yourself. I'm peaky." He starts for the kitchen again and then pauses, narrowing his eyes. "Wait. My laptop was upstairs on my bed. Yours was on the table. Explain to me how mine was closer."

The truth was it hadn't been closer, and Sherlock is caught off guard for a moment.

"So, were you going through my files or just trying to annoy me?" John continues. "Because your computer is about ten times better than mine, so if you want to swap I'm all for it."

Neither, actually. Sherlock does, of course go through John's computer files religiously but always when John isn't home. They are generally a mixture of financial records, in-progress blog posts, and no more porn than is considered usual for a single man of his age. John clears his browser history often, but not very well, at least not for someone with Sherlock's talents.

Sherlock finds pornography tiresome and repetitive and John's choices are always vanilla and hetero without a kink to be found in them, not even a threesome, so much so that Sherlock has to wonder if that's actually his taste or if it's intentionally selected for the appearance of normality like so much about him, like he's trying to convince himself most of all…

He has absolutely no answer for John beyond the undercurrent of unspeakable thoughts which now seems to run constantly in his brain. Thankfully, there is another distraction.

Sherlock shuts the laptop and sniffs the air loudly, standing up and approaching John.

"What?" John says, thrown.

"You've had sex!" Sherlock says, almost accusingly.

"Why would you think that?" John is defensive, even though he must know he's already lost.

"You've showered."

"Yes, I told you I was going to the fitness club. I showered there. After I exercised. As one does."

Sherlock sniffs again, looking faintly nauseated. "You'd better have another. You reek of sex, I can smell it all over you."

He can smell her all over John, a woman, someone common, another one not worth John's time, not worth John's affection…

John rolls his eyes. "You know most people wouldn't put up with this shite, but fine. Not that it's any of your business, but yes, I just had sex and it was spectacular."

Spectacular, of course John would be spectacular, with his strong hands and his gentle manner and his small but rugged body, well muscled and neither to thin nor too heavy…

"No, it wasn't," Sherlock says dismissively, returning to his chair and reaching for the laptop again. John is faster and snatches it up, turning and stalking up the stairs.

"Who was she?" Sherlock calls after him.

"Piss off." The door to John's room slams.

Sherlock is a bit surprised at this development, given that he usually knows when John has someone on the go. Who could she be, why hide her so carefully? She must be someone John really likes and he's afraid Sherlock will scare her off. Or perhaps she's just a shag and he's ashamed of himself over it. The latter option seems more likely, given the time of day and that John would be in a better mood if he had been with someone he actually liked, but Sherlock can't stop himself from thinking the worst.

John's going to fall in love and give his heart away and he won't be able to get it back and he'll leave Sherlock and fade out of his life like he was never here but it won't ever be the same as it was before, John with his honest face and stubborn morality and the little packet of vile ketchup crisps he likes in the afternoons…

Sherlock tries to put the brakes on this line of thought, of the irrational fear that grips him, but fails utterly. He can't quite convince himself that this is just about sex anymore, but he doesn't understand what it is about. He suspects John could explain it to him, but knows that asking him is a very bad idea.