A/N: Don't usually write for this pairing, but they are rather intriguing, aren't they? So; have some smut, everyone. Please review, as well, because I'm still expanding my horizons when it comes to smut so feedback really, really helps.

-for you!

The first time they had sex, Jim started it.

Well, that's what Sebastian always says, anyway, and not least because he knows that if he says anything otherwise, he probably won't wake up the next morning. Jim Moriarty would never do anything because someone else suggested it, and Sebastian is quite all right with that.

That's not to say that Sebastian didn't want to start it; he'd been debating for at least an hour beforehand whether it would be worth losing his left hand – not his gun hand, Jim needed that one intact – just for a touch of the mastermind's lips on his, and had very nearly decided to just go ahead and do it. He's glad he didn't now, of course, because then it would have been a transgression and a punishment and then that would have been that.

As it was, Jim had just finished something extraordinarily difficult that Sebastian wouldn't even dream of guessing at, mostly because he'd be talking about something he doesn't understand and be likely to make a fool of himself. He'd called Sebastian into the room and bounced and shouted around for about half an hour, grinning like a lunatic and calling the sniper all sorts of names that varied from 'bottom-feeder' to 'idiot' to 'darling'. Forgive him if he was a little confused.

Sometimes with Jim there is nothing you can do but stand back and admire him until he calms down enough to let you remember you were supposed to be doing something else. That night had looked like it might be one of those times, so Sebastian had let his thoughts drift somewhere in the vicinity of his boss's arse and what the punishment might be for biting it.

"Sebastian."

It had taken him a few seconds to come back to earth, and when he'd finally blinked himself back to reality Jim's hand was coming down onto his cheek. "Ouch! Jim!"

Jim had smirked. "Did you get a bit distracted by my arse, there, Seb?"

He's always said that one of the reason's he's kept Sebastian around all this time is his habit of being completely honest. Most people pander to Jim like they're afraid he'll have them killed if they say they don't like his tie; he supposes it must be refreshing to have one person crinkle their nose up at it and say something more along the lines of, it's the most awful thing I've ever seen. And I kill people for a living. So faced with a situation where Jim asks him a direct question, Sebastian will almost always be at least partly honest. "A bit."

Other people are quite frequently shocked by the casual attitude Sebastian takes to his boss in general. He's probably the only person in the criminal world who refers to him as 'Jim'. Even more surprising, though, is that Jim lets him. Quite a lot of them probably thought that this sort of thing was going on right from the start, but Sebastian can honestly say that when Jim leaned up and smashed their lips together so hard he almost broke his nose it was not unwanted but almost totally unexpected.

That first time seemed to be almost entirely a one-man affair, and Sebastian was a little unsure of what he was supposed to do. By the time his brain managed to assert enough control over his cock to realise what was happening, he was naked on his back on a table, with an equally naked Jim straddling him and lowering himself slowly onto his cock.

His brain disengaged again to focus all its efforts on not coming. When it grew brave enough to have another go, he reached up to touch Jim's face, the dark eyes almost black with lust, brow just slightly crinkled in concentration, and got his hand slapped away for his trouble. Was he not supposed to touch Jim? The consulting criminal seemed to be using him like some sort of sex toy, sliding slowly up and down his cock and stroking himself. Hesitantly, Sebastian had reached out again, this time for Jim's erection, and been slapped away again. "Jim…"

The smaller man had gasped out a short 'Seb!' and come, shooting thick ropes of semen over his chest that had roughly pushed him closer to the edge; but then Jim was pulling up and away and the pressure was gone, and Sebastian couldn't say he was entirely surprised. Jim always did what he wanted, without a care for anyone else. He waited for his boss to leave so he could close his eyes and toss himself off.

Something warm and wet engulfed his cock and he almost jumped off the table. "Shit! Jim!"

Jim had chuckled and released him with a pop that echoed sickeningly around the room. "Did you think I was just going to leave you like this?" His beautiful, bottomless eyes had swept the length of his body appraisingly. "It is rather a nice view."

He could feel himself growing impossibly harder with his boss's critical eye on him, and he knew Jim could see it, too. Long fingers trailed up one thigh before stroking the nail over the underside of his cock; Sebastian shuddered as his thighs clenched automatically, his hips pumping up to try and squeeze some kind of friction out of the finger tickling just below the head of his cock. "Jim," he'd bitten out again.

The man had smiled, and without warning bent down and taken Sebastian into his mouth again, and it hadn't taken long like this before he was coming harder than he could remember coming before, panting his boss's name and helplessly twining fingers through Jim's dark hair.

Jim had swung himself into a sitting position on the table and grinned devilishly. "Next time, we'll do it slowly." Sebastian had shivered, flushing hot and breaking out into goosebumps simultaneously. Next time.

"Will I actually be able to make love back to you, next time?" he'd asked without thinking.

The consulting criminal's easy grin had vanished, immediately replaced by a hard expression. "It's not love," he'd said, and walked away.

And that was fair enough. It had been more down to poor word choice than anything the first time. Call him old-fashioned, but Sebastian had always called it 'making love', unless it was completely devoid of anything other than a quick fuck with a stranger.

But the second time they had sex, Sebastian called it 'making love' again, just to see what Jim's reaction would be. He was a little bit worried that time, he'll admit, that maybe the mastermind would get annoyed and just give up the whole thing as a bad job; but after Jim snarled at him and told him again, it's not love, he'd decided that he could risk it. Just to show himself that he wasn't completely powerless.

They didn't do it slowly, either. Perhaps Jim had meant to, but he'd turned up at Sebastian's flat in dark jeans and a tight t-shirt, and the sniper had been so taken aback he'd very nearly jumped his boss in the doorway, and after that it had been a mess of teeth and tongues and sweat and there just hadn't been time to slow down.

It's not a coincidence that the first time they did take it slowly was the first time Sebastian started to think that maybe it was love. Until then it had been senseless fucking; Jim would wait until they were alone together – usually, with a few notable exceptions – and grab him and shove his tongue in his mouth and his hands down his pants until they were rolling on the nearest surface with arms and legs and cocks intertwined.

He'd just been out on a job and it was late at night and he'd come home stiff with dried blood; he hadn't noticed until he'd wandered out naked into his bedroom that there was an equally-naked consulting criminal in his bed. "Jim," he'd said in surprise, dropping the towel he'd been rubbing over his hair.

"Sebastian." Jim had lifted a hand and inspected his fingernails, as though it was perfectly natural for him to be there. Like he belonged. And Sebastian had taken a moment before he'd realised that it was actually strange. They'd never done it in a bed before; even that time when Jim had knocked on his door, they'd never made it out of the kitchen.

He was tired, and really the last thing he felt like was the kind of wild romp that Jim usually provided; even so, the sight of his boss naked and hard in his bed was something he couldn't possibly not react to. So he'd staggered over to the bed and lain down next to the consulting criminal, slid his hands up to cup the delicate curve of his jaw and kissed him softly. We're going to do this my way, he'd thought to himself. We are going to make love.

He hadn't said it out loud, of course, not because he thought Jim wouldn't want to have sex at all if he did, but more because he knew that if they were going to do this slowly, they had to do it before Jim noticed it was happening like that.

So he'd taken control gently, rolled Jim onto his back and climbed atop him carefully; he'd taken the time to prepare his lover instead of just driving in like Jim usually liked him to. They'd moved in and out of each other almost tenderly, the space between them filled with soft gasps rather than Jim's usual wild shouts; when he finally reached climax, at his own pace rather than trying frantically to keep up with whatever gallop Jim had set, it had come like a bucket overflowing, gentle but overwhelming, rather than the sudden and blistering orgasms of their frantic fucking.

After, he'd bent down and cleaned Jim's come off his chest with his tongue, listening to the ragged breathing of his lover as the other man tried to sort out his thoughts enough to realise what had gone wrong.

"What was that?" Jim had said finally, his voice soft and dangerous as Sebastian attempted to work the bedcovers out from under the mastermind's arse.

Sebastian had finally managed to tuck them both into bed before he answered. "Didn't you enjoy it?" he'd asked, smirking to himself because he already knew the answer. It was late; he'd reached up and turned off the light.

"And what are you doing now?" Jim had demanded petulantly, sitting up in bed.

"I'm going to sleep. I've had a long day."

The consulting criminal had tried to get up and leave, only to find Sebastian's hand clamped around his wrist. "Let go of me," he spat.

"Or what?" Sebastian had challenged. He'd asked in earnest, because he'd actually been curious as to what Jim's punishment might have been, but his lover had simply huffed in an irritation that Sebastian wasn't sure was entirely real and slumped back against the pillows. The sniper had wrapped his arms and legs around Jim to make sure he wasn't going to leave, and then fallen asleep.

He'd woken up first, which surprised him. He'd never actually seen Jim sleep before, and he'd kind of assumed he was the sort who'd power-nap for an hour or two and then work his way out of Sebastian's embrace and leave. But he woke up to sun streaming through the window where he'd forgotten to shut the curtain – he spared a brief thought for anything the neighbours may or may not have seen last night – and a consulting criminal tucked under his arm and breathing softly against his chest.

Jim's face when he was asleep had been a revelation; he'd looked completely relaxed, without the strain of a thousand murders to orchestrate and cover up etched into premature frown-lines. His hair was mussed and sticking with static to Sebastian's upper arm, and his long eyelashes had brushed against his cheekbones like a spider lying in wait. Sebastian had found himself wishing he could see Jim this carefree when he was awake, to get the beauty of his little content half-smile and still be able to see his dark, Irish eyes.

He'd been in the process of protectively smoothing his lover's hair when Jim had woken up. The consulting criminal had smiled in his first moment of consciousness, but then he'd opened his eyes and realised where he was.

Jim had bolted upright as though the static in his hair had sparked an electric shock. "What are you doing?" he'd asked.

Sebastian hadn't quite been sure how to answer. "I didn't want to wake you. I know you don't sleep often."

He'd jumped out of bed and dug his clothes out of the depths of Sebastian's own wardrobe. "I had things to do, why did you make me stay?" his voice was irate, but Sebastian had seen him that angry before, and now he was starting to get just a little bit fed up himself.

"Because that's what people do," he'd said, sitting up himself and letting the blankets fall off his bare chest. He noticed the way Jim's eyes flickered down to the trail of hair leading under the covers. "They make love, and then they fall asleep together."

Jim's jaw had tightened in preparation for his customary response. "It's not love."

By that stage it had become a customary byplay between the two of them; after sex, Sebastian would slip the phrase 'making love' into conversation, and Jim would roll his eyes and say, 'it's not love'. Now, though, he really sounded angry; Sebastian found himself surprised at the vehemence with which his boss insisted.

The word denial floated around his head in search of a meaningful sentence to connect with.

"Why not?" he'd asked. "Why can't it be making love? What would you call last night, then?"

Jim had frozen with his tie half-tied; Sebastian held his breath while he waited for his boss's limbs to settle into eerie, threatening calm. "If you can't keep emotions out of this, Sebastian, then I'm not coming back."

Sebastian had bitten his lip with nerves, but he said it anyway. "So don't come back."

That was three weeks ago, and they haven't had sex since. He's not sure whether this is what he expected or not; there was a part of him that thought Jim would take this like he took Sebastian's insistence that he stay the night, like he put up with the constant references to making love, and he'd be back within a week. He won't deny that he misses it. He thinks he's maybe known that – for him, at least – this was love for quite a while.

He'll walk into a room and Jim will glare at him. He tries not to react, but he knows that he wouldn't do it if he didn't care, if he didn't miss this too. And the fact that Jim still puts up with him, still trusts him, is either testament to Sebastian's skill with a rifle or the fact that Jim, as much as he's always hated to admit it, has these emotion things too.

When Jim slides into bed beside him in the early hours of one morning he almost shoots him. He keeps a loaded Beretta in the drawer of his bedsit that most people reserve for lubricant; he's rolled over, flicked the light on and shoved the barrel of the gun into the intruder's mouth before he looks down and sees his boss, teeth bared around the metal, grinning at him. He lets out a few swear words and withdraws the weapon. "I do love a man who's good with a gun," Jim drawls. Sebastian rolls his eyes.

He notices that Jim's naked, and he almost employs the dreaded did you bring a gun, too line when he notices that his hand, of its own volition, has snaked under the covers and wrapped itself around the bulge, and the question becomes redundant. That's definitely not a gun.

Jim grins. "I have a job for you, Sebastian," he says. There's too much breath in his voice and Sebastian hasn't heard it like that in far too long.

"Yes, you do," he replies, ducking his head under the covers and taking the erection he finds there into his mouth. Jim arches his back, thrusting his hips gently into the sniper's mouth and sighing. He's missed me, too, Sebastian realises triumphantly as Jim's fingers assert themselves in his hair.

He crawls back up his lover's body and presses tender kisses to his lips. He expects Jim to realise pretty quickly that Sebastian intends to have him slowly again and put a stop to it, but the mastermind says nothing. He almost seems shy, his hands hesitant over Sebastian's chest, complying with every unspoken request without saying anything.

He's too impatient to prepare Jim, and he knows by now that his lover can take it; he hooks one of Jim's ankles over his shoulder, peppers gentle kisses over his chin and neck, and presses into his body.

God, he missed this. Jim's inside is hot and tight, and the muscles ripple and clench along every inch of his cock. He bites his lip until it bleeds and pants into Jim's shoulder until he's confident that he's not going to come straight away; when his lover rocks his arse gently up into his hips he takes the hint and starts to move.

"Oh, God, Jim," he groans, testing the waters. "I've missed making love to you so much."

He leans up for a kiss, but the consulting criminal turns his chin up away from it. "It's not love," he insists, but he's still grinning.

Sebastian bites down gently on Jim's chin instead, glee and triumph flooding his veins with adrenaline. "If you say so."