A vile alley. A heavy door with no signs on it, approached by a steep flight of steps leading down to a black gap. A low room, decorated with dusty velvet curtains and lots of mirrors – an unconvincing attempt to make this den presentable. Sherlock catches a glimpse of his own reflection. Dark curls, dark jeans, tight and low on the hips, the fitted shirt and the jacket are dark too. So suitable for a dark place like this.

A polite, unsmiling young man – do they call him a receptionist? – awaits him already, takes the cash and leads him to a private room at the end of the long corridor ("Follow me, please"). There are muffled intimate sounds behind the closed doors along the way.

The expression on the youth's face is neutral, with no hint of curiosity – a well-trained lad, with a respect for privacy, most appropriate for his job. But he is obviously intrigued. He must have seen a whole lot of clients with extraordinary whims and weaknesses, but no one who would come to the dungeon, as they call this ill-famed fetish club, with his own implements for striking (a whip and a cane, both properly disinfected, for Sherlock is rather dubious about the sanitary norms in the said establishment) and – moreover – with a professional camera and a pack of enlarged photos, black-and-white copies.

Sherlock has been business-like and precise describing his preferences. And very picky choosing a proper dom. Two doms, actually.

The first one, a grim-faced, solidly built lad in his late twenties, emerges from a deep chair as Sherlock enters the room (deliberately ill-lit and full of mirrors, just like the lobby, and with a wide bed as the centre of attention). The receptionist leaves them both to their own affairs.

The whip and the cane are laid onto a table beside the bed, within easy reach. Sherlock holds out the camera to the dom, thoroughly instructed in advance (no need to remember his name, this information is quite irrelevant, and no need to talk to him either), strips off his jacket, and the shirt too – a quick dance of fingers against each button, then takes off the shoes and socks. The thick carpet is comfortable enough to stand on.

The dom would prefer to see his client fully undressed, judging by the appreciative look he gives the denim-clad backside, as Sherlock gets up onto the bed, and surely not only because he likes the style of Sherlock's jeans.

You've been well paid, no bonus points for you, Sherlock thinks wryly, stretching himself and holding on to the headboard with both hands, as if he is tied up to it.

"Take a test shot."

The lighting is poor. Probably, he will have to adjust exposure.

The flash fires.

He checks the results on he camera screen, sitting back on his heels. Not so bad, despite his doubts. The guy is really experienced in taking pictures. Fine.

"Let's start, then. Look at the photos once more. Exactly the same pattern, remember."

He turns the camera off, lays it onto the table and braces against the railings again, freezing in the same posture. In the mirror above the bedpost his dom raises the whip and lets it fall.

A line of stinging pain explodes across his back. A sharp tingle at the wake of the impact tells him that the blow has been hard enough to break the skin. Excellent.

The lines multiply quickly, one layer of pain after another. The whip cuts into his skin again and again, till he is gripping the thin wooden slats of the headboard so desperately that he can probably break them.

But he won't stop this.

That's the best way to get what he needs.

Then comes the cane. The young dom suddenly gets somewhat hesitant, surveying Sherlock's back, marred with stripes, frowning thoughtfully and tapping the flexible cane against his palm – thud, thud, thud. Sherlock can see his face in the mirror. Too much visible damage, that's what he must be thinking. Won't the client complain afterwards? The lad licks a tongue briefly across his lower lip, a sudden unwelcome reminder – John does that sometimes, quite unconsciously, when he is a little bit nervous.

"I won't complain," Sherlock says harshly. "Go on with it. Just two blows. Quick and hard."

One. A sharp urge to cry out. Two. Not as bad – but still a lancing sensation across the ribs, making him quiver involuntary, without a sound.

Now, a few close-ups.

He plays the pictures back, zooming the images, ignoring the itching pain the slightest movement causes him. The cuts are deeper than it is necessary, but that will do.

"Good. Come back in half an hour. Bring the other dom with you."

It's better to delete this half an hour afterwards, just like an unwanted picture. He hates to wait. He hates that smell of cheap perfume from the sheets. He hates himself for wanting to groan in the pillow, though he knows perfectly well that producing any sounds doesn't ease the pain. And, most of all, he hates the thoughts that keep floating through his mind. He can't stop imagining John's face – what it would look like if he saw this den, this room, with Sherlock fitting here so well.

It's not that he cares what people think of him. Including John.

He's just… well, he's just glad that John won't know anything about it, for he is going to return home much later in the evening, spending it with some rugby lads from Blackheath.

Finally, the young man comes back, bringing a woman with him, lean and sylphlike, dressed in leather that doesn't become her in the slightest.

"You first," Sherlock tells the guy. "Two more strokes with the cane, just above the previous ones."

A series of shots follows afterwards, and then it's the woman's turn. Another two strokes, across the raw whip cuts and closer to the neck. They are applied with less force, as he has expected, but almost bring him to a shaky condition nevertheless – he is panting and clenching the railings uncontrollably for a while, his lower lip bitten on one side. Too much impressions for today.

More shots again, as his breath steadies slowly.

And it's over at last.

Sherlock scrolls through the pictures in reverse order once more, watching the welts and blood patches disappear from his back, till it's marble white again when he reaches the first image. Back to purity, huh.

He will probably leave the cane and the whip here, these pictures are quite satisfactory, no need to repeat the session.

He puts on the shirt and the jacket, gritting his teeth. Bending down to grab the shoes is not a good idea, the movement makes him hiss, but he declines the woman's persistent suggestions to call a doctor ("A very discreet one, you know. We have all kinds of accidents here sometimes"). He'll manage to cope on his own. He needs to get home – and then he'll cleanse the cuts somehow.

He doesn't want anyone to witness the process.

As the cab drives through the endless succession of sombre and deserted streets, he tries his best to divert from the pain. It's not unbearable, in fact, but very irritating. His abraded shoulders burn badly if he leans back. And balancing in the swaying taxi, without leaning to something, is equally uncomfortable because the sore welts tend to stretch all the time.

Everything but the brain is transport… only when this transport system works as it should. When some tiny parts of the structure break, all you can think of is the throbbing ache that makes you so human.

He should have taken painkillers with him. Co-dydramol, for instance. Or something stronger.

So stupid.

But it's nice to have something to look forward to.

All he wants to do is to fall on his own bed, lie there flat on the stomach, numbed with medication, and spend a few hours like that before sending the pictures to Lestrade.

Internet is a bliss. At least, he doesn't have to see that "oh-man-you're-fucked-in-the-head-and-as-if-I-didn't-know-that" look on Lestrade's face. Lestrade puts up with his extraordinary methods, as long as they are efficient and helpful, but always shakes his head, uncomprehending – are you really crazy, Sherlock?

Oh hell, what does it matter if he is ready to do something reckless to prove his point?

And he does have the proof now.

It was not the professional dom who broke the neck of Neil Gibson, a rich and successful businessman, a strong, ambitious person absorbed in his work, with his own empire to rule, but with some weaknesses too, rather unseemly ones for a respectable member of high society. He has always been discreet leading a double life, though, dividing his free time between his spouse, presentable and smart enough to accompany him to corporate events, but otherwise neglected, and a young handsome dom, muscular and solidly built, who visited Gibson regularly in his decadent bachelor apartment. The youth swore that on the day of Gibson's death he had left his sub flogged with a whip (not a cane that was proved to be the murder weapon) and alive, tied up to the bedpost, according to his usual wish… He intended to return in a few hours. But by that time Gibson was long dead.

Everyone assumed that it was just the BDSM play gone wrong. It's so easy to close the case. But the timing and the force of the impacts suggest another hand. A feminine hand, most likely. Gibson's little wide-eyed widow, with her well controlled hysteria, has something to hide. Sherlock can imagine the crime scene quite vividly. She has tracked her husband down, fostering suspicions, and found him in a very compromising position. There must have been a quarrel… mutual offences hissed and their whole life called a fake… one of the various striking implements at hand ("Do you like pain? Is it what you want, you bastard?")… And a cane like that is heavy enough to damage the spine as it hits the neck accidentally.

No experienced dom would allow such a violation of safety rules.

The woman's guilt is yet to be proved. The pictures won't count as evidence – but they will make Lestrade reconsider the case. That's a start. There is a small part of the puzzle Sherlock still doesn't understand, but it has nothing to do with the murder. He will think of it later.

Sherlock finishes the journey completely exhausted but more or less content. The cab drives away, as he keeps searching for the keys with an economy of motion, the strap of the camera cutting into his neck, damn it. He has to sling it over one shoulder, feeling every millimeter of his bruised and grazed back.

Soon he'll be able to switch himself off for a while, after undergoing the necessary ordeal of cleaning the cuts. He sighs almost peacefully, going up the stairs.

But there is an unpleasant surprise for him. The sound of footsteps in the kitchen.

John is at home too. Damn. Damn.

John's presence is most undesirable not only because Sherlock is not in the mood for any explanations, should his flatmate notice something strange, but also because there's no chance to borrow John's medical kit without being caught red-handed. The mere thought that he will have to go out again, and trudge to the nearest chemist (and "the nearest" doesn't really mean it's the next door down), and stand in the inevitable queue, and face a cheerful girl on the till… no, it's completely and utterly appalling.

Maybe he's got aspirins, somewhere in the bathroom.

"Sherlock, is that you?" The sound of water pouring into a mug. A creaking noise, like the one of the cupboard doors being opened at random and closed again.

"I thought you would be still hanging out with your… friends," Sherlock says, carefully placing the camera onto the desk, next to his laptop.

"I thought that too," John mutters from the kitchen, clearly upset. "But I don't fit in anymore somehow. I mean, they're nice chaps, really. The thing is, it doesn't seem like fun to me downing pints in the pub and taking the mick out of each other, just like we used to, before my commission. Maybe I'm getting too old."

John appears in the doorframe with a mug in his hands, pale blue shirt unbuttoned, a plain white tee under it, and Sherlock leaves the room hastily, dropping a brief comment without looking back: "It must be my deleterious influence, that's all."

There's a soft chuckle behind him. Much better.

Any other day, he would have been glad to see John at home so early. It's so interesting to tease him with wry and snide remarks, turning his depressive sadness into healthy vibrant irritation.

But now Sherlock should be careful not to catch his eye. John is observant enough, and that's pretty inconvenient sometimes. The evening may end up with an uneasy conversation, if mildly put. Especially after that recent row when John saw his left hand all mottled over with small pieces of plaster… He just needed blood samples. And he disinfected John's scalpel afterwards, so why making a fuss?

In the bathroom Sherlock lowers himself wearily on to the ledge of the tub, trying to shake off these recollections.

Gibson's case. Concentrate on Gibson's case.

The only thing he still doesn't understand – and it bothers him like an itch – is not the murderer's motivation but the victim's. Why would an ambitious, successful man, so impetuous and harsh outside his bedroom, enjoy being a sub? It's slightly out of character, isn't it? But all the data indicated that it wasn't just a one time deal. Gibson had a sort of relationships with that unfortunate dom.

Theoretically, Sherlock can get the appeal of the flagellation process. Some people may be experiencing a very intense emotional high when the violated body is building up endorphins, along with adrenaline. (Though in practice, he felt nothing but the pain itself. It was just mechanical damage. The whip breaking the skin, the cane crushing deeper tissue and the blood vessels running through it…) Alright then, Gibson could be getting off on extreme impressions. But the whole concept of submission includes not only corporal punishment. All these games with being tied up, admitting someone else is in control… how could a self-sufficient man like Gibson get involved in this stuff? It's hard to imagine that he hasn't been commanding from the bottom all the time, but apparently – he hasn't…

Sherlock forces himself to get up and to search the cabinet over the sink. Here's the bottle of aspirin, but it's empty.

No painkillers. No antiseptic solution. He should have bought his own first aid kit a long time ago but it's always so tempting to borrow John's while he is away…

The only thing he can do is to clean off the dried blood. By now, he's not sure that he will be able to tough out a shower, splashes of water against his shoulders. A wet towel, then.

The jacket is gingerly taken off and tossed onto the laundry hamper. It's somewhat more difficult with the shirt. The fabric has stuck to the cuts. Pulling himself free, he feels that these crusts slowly tear open and lets out a curse.

"Sherlock?" John's voice comes from behind the door. "Are you alright?"

The door is still unlocked. Oh.

"Fine!" he exclaims, crumpling the shirt in his hands.

But it's too late. When John is worried (and yes, he often has reasons for being apprehensive, since the very day he's moved in), he shows no respect for privacy.

The door swings open.

Sherlock knows how he must look like. Nasty. The lower lip bitten, starting to swell. The red, diagonal marks of a whip across his shoulders. Multiple bruises…

"Problem?" he asks with cold politeness.

"Christ! Your back!" John exhales. "What happened?" Clearly, his first thought was of an assault. It makes everything worse because here they come to an awkward point. No criminal is to blame. It's even harder to explain himself than Sherlock has imagined because John is so anxious, so genuinely troubled… The expression on his face will be changing soon, gradually, from "Sherlock-are-you-alright" to "Sherlock-what-have-you-done-to-yourself". From sympathy to incomprehension. Bewilderment. Disapproval.

It's easier to ignore what you don't see at all. You'd better send him away somehow, even if it means being rude. Cut him off with a caustic remark – right now, at once.

If John thought that it was a kind of sexual kink, not an experiment, would he leave, feeling confused? Sherlock hesitates, quickly running other options in his mind, but this one seems to be the best choice.

"Don't worry. It was quite consensual," he says with the most unpleasant smile he can manage.

"I see. A nice evening out," John nods slowly, still staring at him rather dubiously, somewhat taken aback – but with no intention to leave.

"A sort of. My private affairs. No concern of yours."

John's lips tighten. Of course, he'll be offended by this rudeness. Shocked. Sullen for a while. But at least, he will ask no questions, for he's a tolerant man. And after some time they both will be able to pretend that nothing has happened.

"Now, John, would you close the door?"

And… so he does.

End of story.

Sherlock leans to the tiles with fisted hands, fighting the dizziness and telling himself not to slide to the floor, though the idea seems very appealing.

He thought it wouldn't be that easy to force John out. All of a sudden, he feels so lonely – abandoned – that it hurts almost physically, making him whine through the gritted teeth in anger for himself. It's illogical. Childish. He wanted to be alone, it's better to be alone. He should be thankful that no one will watch him wincing and writhing, so weak and bloody pathetic. He needs no condescending pity. No lectures.

But sometimes his whole life resembles that ride in a swaying taxi, with no one to hold him while he is aching and bleeding and feeling so miserable that it makes him more and more exasperated.

He turns on the taps.

Stop thinking.

As the door opens again, he must be looking truly surprised, for John, carrying his medical kit and a chair from the kitchen, snaps with a hint of anger in his voice: "Did you think I'd leave you like that?"

"John, you don't have to…"

"No one asks for your opinion," John growls. "Sit down. Face to the backrest," and his tone is so firm that Sherlock obeys without further argument.

"Did you take anything?" John demands. "No?"

He disappears again and comes back with two pills and a mug of water: "Here."

Sherlock swallows the pills and puts the mug on the shelf of the sink, while John takes a closer look at his sore back.

"Shallow cuts. No need for stitches, lucky for you. Now, I'll clean the blood off."

At the first sting of the antiseptic solution Sherlock shudders convulsively with a stifled moan. It's so humiliating, disgusting that he can't pull himself together anymore... But John stops for a few seconds, his hands resting on Sherlock's upper arms, squeezing them slightly in reassurance, and this sudden and simple physical tenderness makes his heart clench. Oh, John.

After that it's better.

It's not a challenge, or a test of strength. He can relax into this pain, flow along with it, very near to the meditative state, because it's John, and he knows what to do, and he won't hurt more than he should – but even if he does, it's alright.

John swabs blood with sterile gauze soaked in antiseptic, moving with a brisk gentleness, so neat and quick. His touches are light, but very personal in some way. A connection between them. And Sherlock doesn't mind being weak just this once, giving up his control, and placing himself into John's hands – literally.

Maybe that was the attraction Gibson found in submitting.

"I can use arnica on the bruises..." John says at last. And then adds, quite inconsistently: "You took pictures."

It's like a lash, hard and unexpected. An accusation. The strange weakening feeling of safety vanishes swiftly, all the defensive walls are built up again in a haste. Sherlock doesn't look back, reluctant to meet John's gaze.

"The camera on your desk. You took pictures for Lestrade," John continues flatly. "No idea why, but don't tell me that it's not for another case. I know you."

Finally. Time for a lecture on inappropriate behavior. But Sherlock can enumerate all the arguments already. A self-destructive freak, that's what people normally call him. Well, yes. Is that news to you, John? And now what? Will you recommend me to see a therapist? But that doesn't help much, as you can tell from your own experience.

John pauses, then goes on tentatively: "I have a question for you… If you couldn't take the whipping yourself, no matter why, would you do that to me, for the sake of your case? Against my will? If I begged you to stop?"

What a nonsense.

"John, how can you even…"

"But that's what you do. How do you think I feel when you come home like that? I can only wonder what it will be the next time, how you'll be torturing yourself just to prove you're clever. For this is how you get your kicks, isn't it? I know that you don't care much for your own wellbeing, but I do. It's maddening, absolutely maddening, always. An agony. And just so that I know, does that bother you at all?"

The words are bitter, desperate, and Sherlock suddenly feels his chest tightening.

"John…" He wants to say something hatefully pedestrian like "I'm sorry", but his voice breaks – and all he can do is turn back and bury his face in John's t-shirt.

And so they stay like that for a while, both slightly confused, but somehow it's fine, because John keeps stroking his hair, one hand resting on his nape.

Finally Sherlock looks up, tousled and messy.

"You know," he says thoughtfully, "you could be a surprisingly good dom, strict but careful, and with that military doctor commanding voice."

"Sure," John responds in the same casual tone, even if a little bemused. "Most doctors are doms by nature, otherwise no one would listen to them."

And a second later they smile simultaneously, as they often do.