They're probably not even supposed to be in here.
Though Sherlock never pays attention when people tell him he isn't allowed to be in places. Even Mycroft, whose places have always felt more secretive and dangerous than even Sherlock's.
Sherlock can probably be anywhere he likes with impunity.
John's the one who feels out of place.
Mycroft's main office is...it's big, and ever so slightly terrifying. It's immaculately organised and it has no windows. Though it does appears to have its own library. Sherlock has perched himself on the edge of the desk, scattering pens and several dozen important looking files across the leather surface.
"Aren't you worried in the slightest that Mycroft will come back?" John asks, trying not to touch anything, or wander anywhere where he might touch anything.
"He won't, he'll be somewhere else doing something tedious with other terribly dull people who've never had a spark of excitement in their dull little lives." Sherlock rifles among the contents of the desk with an air of terrible boredom. Leaving everything in horrible disarray. "He won't be back for hours."
Sherlock tips his head down, expression strangely and suddenly focused.
"Hours," he offers, like that's supposed to mean something to John - and then it does and he's trying very hard to make his expression tell Sherlock that, no, absolutely not.
But Sherlock is already all movement and purpose, tugging him forward by the edge of his coat, and John's back hits the desk with a thud.
"Sherlock, we're absolutely not doing this here - we're not -" John has to stop because it's impossible to talk when Sherlock's kissing him.
Something hits the floor with a clatter, possibly something expensive. Sherlock is wrecking the expensive things in Mycroft's office and John isn't doing anything but trying vainly to convince Sherlock that this isn't the time, or the place, when his mouth is occupied and his hands seem intent on ending up inside Sherlock's coat anyway.
"Yes," Sherlock decides against his mouth, like he gets to make the final decision on everything.
"Just because something seems exciting doesn't mean it's a good idea," John says, which would be more effective if Sherlock's wasn't already mumbling disagreement into his throat while at the same time trying to fling his coat off. It's a lot of coat to fling but Sherlock manages it.
Something hits the floor with a thud.
They're clearly in a rush.
"Are you afraid he'll come back and critique your performance?" John offers, trying not to laugh, because Mycroft's a lot less terrifying when he's not actually present.
Sherlock grunts like he's afraid Mycroft will do exactly that.
John ends up laughing even though he doesn’t mean to, all messy noises under every push of Sherlock's mouth.
"Should I be afraid he'll critique my performance?" he asks, when Sherlock pauses long enough to tug John's coat off and throw it over the chair behind them.
Sherlock's hands are suddenly firm and insistent on his waist, swivelling him before he has a chance to protest.
John's hands slap the desk, scattering paper everywhere. The paper's probably important. But Sherlock is already muttering about how John's too short and this is going to be awkward. He would complain but Sherlock is biting and it all ends up as an exhale, and possibly a swearword or two.
"I'm busy, go away," Sherlock says, irritated, and it takes John a long confused second to realise that he's not talking to him.
When he looks up the first thing he sees is the straight line of an umbrella. The second thing he sees is the hand wrapped around it.
John tries to stand up so fast he suspects he nearly breaks Sherlock's nose.
"Strange, I was under the mistaken impression that this was my office," Mycroft says calmly.
Sherlock makes an irritated noise. "I should have known you'd make an exception for John, stupid of me not to take that into account."
"It's impolite to keep people waiting," Mycroft agrees, giving the impression that Sherlock doesn't fit into that category, that maybe he fits into another, special category.
John's trying to work out how to get Sherlock's hands out from under his shirt in a way no one notices. Considering the company he's in that's probably impossible. Mycroft drops his eyes briefly, looks straight at him and yes, he's officially in that strange place between guilty and embarrassed that will haunt him for years.
"But I see you managed to find a way to pass the time."
Sherlock's hands move, one sliding grip that leaves them higher under John's shirt instead of out of it.
"Consider it payback for all the times you've shown up unwanted in my business," Sherlock says sharply.
Mycroft's eyes manage to slide over and take in absolutely everything without any visible reaction.
Then he sighs and settles into his desk chair.
"Very well, carry on."
"What?" John manages numbly and isn't entirely surprised when everyone ignores him.
Judging by the drop and slide of fingers into his jeans and the cursing to the world at large and Mycroft in particular Sherlock fully intends to carry on. As if this isn't the most obscene and inappropriate thing he's ever done.
But now Mycroft's watching and John didn't - fuck - he didn't sign up for this.
"Sherlock," John's voice comes out shocked. Some variation of 'stop' caught behind his teeth, just waiting. But he hasn't said it.
Sherlock is still pushing his shirt out of the way, if anything more insistent now that his brother's in the room.
"Sherlock," John tries again, breathless, like this is some ludicrous parallel universe where Sherlock hasn't noticed. "What are you doing?"
Or, perhaps more importantly, 'why are you still doing it?' John's not sure why that last part doesn't make it out.
Mycroft looks for all the world like Sherlock when he's contemplating some sort of interesting and vexing problem, only the face is wrong.
"Keep up, John," Sherlock says. As if he's the one who's suddenly being unreasonable.
And then his jeans are sliding over his arse and the noise that comes out of his throat is strangled.
What the fuck are they doing?
John wonders why he hasn't, at the very least, lost his erection because he's not the sort of person who's ever wanted to be watched, at least not before today.
And of all the people to - he finds himself staring at Mycroft without meaning to. The umbrella's now tilted against the desk and his hands are laced in front of him, perilously close to John's own spread fingers.
Sherlock doesn't seem thrown in the slightest, voice still quietly demanding into his hair. His hands slide up under John's shirt again, careless and intent at the same time. Fingers drag over his ribs, pinch his nipples.
John whimpers, audibly.
Mycroft's eyes fix on a point over John's head, and John knows he's looking at Sherlock. Looking for something. After a second Mycroft’s hands unlace. John watches the sleeve of his jacket slide back, watches the hand lift in one careful movement. He feels like he waits forever for the pressure against his mouth, the warmth of fingertips. The slow drag-slide of them across the line of his lower lip is a barely-there sensation which still steals all the air in his throat. It's ticklish and curious, faintly scandalous. Because John's always assumed that Mycroft only touches people to find out things. Touches them to see how they work, to see how they can be broken.
He should - oh god - he should pull away.
He should -
He's waiting for Sherlock to tell Mycroft to stop touching him. Because Sherlock is possessive at the best of times. Childish and vicious in a way John is doing very badly at convincing him is 'not good.' But Sherlock doesn't say a word, instead there's a strange, forced stillness, the slow tension of his fingers and a rush of air that sounds shocked. Sherlock brought him here to flaunt him, to show him off in the most petulant and childish way possible. And instead - Mycroft's thumb curves round John's jaw and it's slow and impossibly intimate in a way it has no business being. John exhales against his fingers, which turn, tilt his head up.
Sherlock's angry and jealous and - by the feel of his clumsy fingers - more turned on than he knows what to do with.
God he must hate that.
John tries to think of something to say, anything - he thinks for one mad second about protesting. But then Sherlock has a finger inside him and any hope that this wasn't going to go too far disappears.
John's aware he's probably bright red, half shame and half guilty arousal and he knows damn well Mycroft sees it all. He's too sharp, too good to miss anything and John's got nowhere else to turn, nowhere else to look.
"He's mine," Sherlock says, soft and dangerous. It's a warning, all vibration and heat that leaves John shuddering and not protesting the slow push of another finger at all.
Mycroft makes a noise, something like agreement but it's far too quick and too easy. It sounds like he wants Sherlock to prove it.
"Fuck," John say breathlessly. Because he feels like he's in the middle of something huge and complicated. Something that's been going on for years. Something he's irritatingly unprepared for. He should be angry, should be anything except confusingly aroused.
But he has no intention of being a prize to be fought over.
The next time Mycroft's fingertips press into the curve of his mouth John tips his head down and takes them inside, lets them slide across his tongue. He shuts his mouth around them, dares to suck once, sharply.
Mycroft inhales, it's quick and rough, like he hadn't expected that. A sliver of perfect human reaction. Which is a heady sort of rush, enough that John presses down just fractionally with his teeth.
It occurs to him that this could be considered inappropriate behaviour since Mycroft is Sherlock's brother. But since Sherlock is currently doing his best to fuck him over the desk where exactly the line of inappropriate behaviour is has become a little fuzzy.
There's no doubt at all that Sherlock is getting off on it. On all of it.
John's not sure if he should be insulted, turned on or terrified.
He settles for all three.
Sherlock works a third finger inside him, which is a slow stretch of discomfort and greed that John wants to protest against but can't - can't because he wants it too. He has to open his mouth because he can't get enough air and Mycroft's fingers slide free, drag wetly across his lower lip and jaw.
John misses them instantly, tongue strangely numb against the roof of his mouth.
"Sherlock," he says, because his mouth is empty and he can.
Sherlock decides that John's more than prepared enough. He presses into the back of him, a familiar collection of smoothness and angles. He's all impatience and clumsiness and sudden pressure where his fingers were so recently. The imperfection of his need is so Sherlock.
John's hands slide on the desk and he gasps, because it's one solid push that leaves his body curved over, helpless to do anything but feel it all. The slow, easy sink all the way up and in.
John wants to let his head fall forward, wants to lay across the desk and brace himself. He wants to - Mycroft leans forward, fingers curling around John's wrists, and his hands stop sliding on the leather surface of the desk.
John's hipbones curve and press into the wood, which is a suggestion of pain that's just enough to keep him thinking. Little sparks that make him wince and gasp.
Mycroft's grip is strong and tight and he's close enough now that John's breathing into the side of his throat. The hard edge of his shirt collar. He's close enough to feel the warmth of him, and he can smell him, something subtle and expensive.
John can't move and he doesn't care.
Sherlock is already moving.
John gasps, open mouth sliding up the warm curve of Mycroft's throat on every sharp thrust, smooth under his own, almost perfect, and this is the closest he's ever been. Closer than he ever imagined he'd be.
He tilts his head just a little, the hard line of Mycroft's jaw a drag of sensation against his mouth.
Mycroft's fingers tighten on his wrists and he turns his head. John doesn't even stop to consider it, he tips his head up. There's no tentative beginning, no testing the waters. They're just kissing, open and aggressive and almost too warm. Nothing John thinks he could ever win, but, god, he can't help trying, and this is an intimacy he never expected.
Mycroft makes a noise in his throat, something soft, like this is a liberty he hadn't intended to take. He doesn't refuse it though, and John's already half-clumsy with arousal, so there's nothing civilised about it. There's nothing elegant here, nothing like John would have expected, if he'd ever thought about it.
He wonders if it even matters because he's kissing Mycroft.
He's kissing Mycroft while Sherlock fucks him and this is definitely not what he expected to be doing today.
Sherlock's nails are brutal in his skin, pace forced into something slower, something hard and punishing but restrained. Like this is an experiment he wants to watch, but he doesn't trust himself to do right. Or maybe John is the experiment, maybe it's his experiment.
He doesn't know.
He can't think any more.