The first time it happens, Sherlock doesn't even notice.

John's brought home women (and men) before, and as far as anyone can be said to have a type, John Watson does. Tall, usually; slim, usually; hair and eyes all over the spectrum. Rare enough Sherlock ever sees them, as John brings them in past the sitting room and hustles them back out again before Sherlock opens his bedroom door. Once in a while, though, someone pokes their head in the sitting room to take a look around the flat – John's quick to blame the mess on Sherlock – and waves before being pulled away, giggling, by John.

So it's highly unusual the day Sherlock damn near knocks flat a woman leaving the loo around 10 AM – late for John, early for Sherlock. He's barely awake and rubbing the back of his head when he leaves the bedroom and makes his way down the little hallway to the shared bathroom when the door pops open and a young woman steps out right into him.

"Oh, sorry!" She sputters. "Hope I didn't wake you. Excuse me, I'll just be going…" and away. Sherlock just waits, looking her up and down once, noting the long dark hair, slim, pale form and grey eyes almost at a level with his own. Creamy white thighs peek out from under one of John's dress shirts crookedly buttoned. Nurse, Sherlock thinks. From the surgery. Took him long enough. With the amount of perfume clinging to his white coat when he comes home, it's a wonder he hasn't bagged half of them by now.

Sherlock mentally shrugs and closes the bathroom door behind him with a snap.

….

Next week, Sherlock's scraping unintelligible sounds from his violin when he hears a thump and a laugh. John had left earlier, gone down the pub to watch a match for the evening, leaving Sherlock to his thoughts. The Blessington case isn't going well, and more than once Sherlock's almost strangled Donovan with his scarf after she's ignored him. In other words, now isn't the time for John's romantic shenanigans.

Sherlock drops his violin on the sofa as he reaches the sitting room door in three long strides and throws it open. There, at the bottom of the stairs, is John, leaning with one arm braced against the wall along the side of a tall, thin man in black jeans and black tee shirt. John's other hand is curled around the man's neck, skimming lips across his cheek before settling in for a passionate kiss, threading his hand through the man's dark hair. Sherlock absorbs all of this in an instant, including the man's (boy's, really, honestly can't be more than 22) aquiline nose, high cheekbones, and startling blue eyes, then shakes himself into action, acid dripping from his words.

"Do you mind? Some of us are actually working, instead of wasting time trying to get a leg over with someone barely half your age and likely using you to make his boyfriend jealous."

John's head snaps up. "What in the actual bloody hell is the matter with you?" John's paramour looks at Sherlock with confused eyes, then back to John, wondering just what kind of lunatic John lives with. "Do you mind?"

Sherlock stops, takes in John's kiss-swollen mouth, mussed hair and slightly-askew jumper, shakes his head, and slams the door.

…

"John," Sherlock calls. "Stop wasting your time chatting up the PC and verify Anderson's time of death. The man wouldn't recognize the signs of previous cold storage if it hit him over the head."

Sherlock watches John offer an apologetic smile to PC Claussen , who laughs carelessly and hands John back his mobile phone. "Later," she whispers, smiling, her green eyes sparkling. She turns back to the police line and the streetlights flash over the coil of dark hair tucked under her police-issue hat.

"Really, Sherlock," John fumes. "I was having a perfectly nice conversation with an attractive woman. Most blokes would help a fellow out and…you know what, never mind." John sighs and turns his attention to the ice-cold body tucked behind the skip.

Sherlock watches him taking temperatures, checking the state of rigor, examining the body's eyes, neck, wrists; and thinks of how methodical John is when he's in his element. Efficient and quick, touch delicate and sure. His mind's eye flicks back to those same hands slipping over a pale neck in a darkened hallway and shudders slightly. John looks up at him, concerned.

"Cold, then?" He strips off his gloves as he stands and looks around to find a place to bin them. "Let's stop at Angelo's on the way home, yeah? I'm craving his bolognaise."

Sherlock only nods.

….

In retrospect, looming up behind your flatmate's date while they're having dinner at the hot new fusion restaurant probably isn't the best way to induce him to accompany you to a crime scene. Under most circumstances, Sherlock would text, but he found himself with an almost disturbing desire to see John's date for himself. After the incident with the young man in the hallway and PC Claussen, John's been even more circumspect than usual, never bringing anyone home and certainly not trying to pick anyone up within view (or earshot, for that matter) of Sherlock. Sherlock's mind has been picking away at this conundrum on a very base level, never allowing it to rise too close to the surface until tonight. Tonight, when he deduced John had a date.

The restaurant's décor is very understated and posh. Reds and golds intertwine through the furnishings and over the walls, complete snooty waitstaff and a large wine list. Not John's usual style at all. Probably more than he can afford, even with a few extra hours at the clinic. Sherlock is interested in who could induce John to stray so far from his usual path.

He spies them across the room and pauses. John's back is to him, so he has an opportunity to observe quietly for a moment through the screen of a large potted palm.

She's a beauty, he'll give John that. Ivory-skinned and trim with a soft fall of ebony hair and a ten-thousand-watt smile, which she's bestowing on John with fairly startling regularity.

He's seen enough and slips along the edges of the room so he can walk up to the table in John's line of vision. He can read the exasperation in John's eye roll and the droop of his shoulders. The woman turns her head to see what John's looking at and squeaks in surprise at Sherlock standing directly behind her.

"Come, John, Lestrade is waiting for us." He holds out his phone so John can read the summoning text.

John rakes a hand over his face and addresses his date. "Pardon me for a moment, please? I'll be right back." He grabs Sherlock by the arm and drags him across the dining room to the loo in the back.

"You're unbelieveable! What in the name of God makes you think you can just summon me like some kind of on-call personal assistant?" John's obviously furious, red faced and gesticulating. "Do you have it in for my dates these days, or what? I haven't had a date in months that you haven't stepped on! I do, occasionally, want to socialize with someone that actually has never, in their entire life, seen a dead person or a crime scene."

Sherlock, not in the least abashed, simply swirls his coat around him as he turns, trusting John will follow him, as he usually does.

And he does. …

He's not sure when he decided that figuring John out was the best sort of challenge, but the idea that there's anything he doesn't know about his flatmate grates him. Seeing John's date at dinner the other night has confirmed at least one thing – John has a type. Women (and men, his mind whispers) that are tall and thin, with dark hair and a porcelain complexion. He's not sure that was always the case, but at least recently, he's been gravitating to the same type of person.

Sherlock looks in the mirror over the sink in the half dimmed light of the bathroom in Baker Street. He's not used to examining himself quite so minutely for any reason other than to be certain his collar is laying properly and his shave is clean.

He turns his head to the right a little, leaning with his hands on the sink, peering into the glass as if it holds the secrets to the universe. Well, perhaps not that important, but some confirmation of a theory he has barely allowed himself to acknowledge would be helpful.

"It's fine. It's…all fine."

He starts with his hair, dark ebony curling over his forehead and ears, longer than it probably should be but he thinks it lends a certain air. Green-grey eyes, luminous as the moon. Pale, pale skin that rarely sees the sun. One or two moles here and there. Tall, always been tall, even as a child. Trim, also, from all those chases across London, but John does that too and he's not quite…

Sherlock stops.

It would seem, after all, that he has more insight into John's dates than he realized.

…..

John looks over the darkened pub, only half-listening to his companions' chatter over the most recent election. He's met up with this group on occasion; a mix of staff from the clinic, and while under most circumstances their animated NHS discussions and office gossip are entertaining enough on their own, tonight John is having a hard time paying attention. It's been a while since he's managed to chat someone up properly, much less take them home. And with Sherlock crashing all of his dates lately, he's not sure he really wants to try. But, quiet evenings have been rare of late, and he's a bit lonely, to be honest. Sherlock ducked out early this afternoon, muttering under his breath and carrying a large, brown-paper wrapped parcel under his arm. John has learned the hard way that ignorance, in some instances, is bliss, and didn't ask about the package or its destination.

Now as he looks over the room once more, his attention is arrested by a tall, slim, dark-haired man leaning casually against the bar. John's almost positive he wasn't there 2 minutes ago. Before he can stop himself, he's already across the room.

"Hello, there."

He smiles, a slow, lazy smirk that sets John's heart fluttering. "Good evening."

"Can I buy you a drink? Looks like you could use another."

"Perhaps. Or, instead of wasting our time here, we could retire to a more…comfortable location."

John smirks and takes Sherlock's glass from his hand, fingers lingering in a caress over his wrist. John steps closer, leans up to whisper in his ear.

"Is that an invitation?"

Sherlock draws a sharp breath and nods.

"Good. Because I think you're just my type."