Sherlock Holmes is a man who sweats.

Working out, running, fencing, or simply standing around waiting, if the temperature is above a decent 20C, moisture will form on the back of his neck, drip down his forehead, and stain the front of his shirts where they cling to his stomach.

And when it's 27 degrees, as it is right now and the only fan John had managed to rustle up from the basement is turning lazy circles in the window, he sweats a lot. A bead of water drops off the end of a curl and down his collar and he shudders, disgusted.

John, on the other hand, is a picture of perfect coolness, his skin smooth, his neck dry. He sits in casual repose, pecking away at his laptop, probably typing up another ridiculous blog post. The collar of his perfectly smooth, perfectly green tee shirt is even perfectly dry.

Sherlock hates him.

"Don't you ever sweat?" he asks peevishly, and wipes a towel across the back of his neck.

"Don't be ridiculous, of course I do. Everyone does. Just still used to the heat, I suppose." He turns in his chair. "Wow. Well, not in the quantities you do, though." John snickers and turns back to his computer.

"Shut up," Sherlock says, and stalks off to the bathroom to take a cold shower.

"Think I'm going to die," Lestrade says, and flutters his shirt away from his chest in a futile cooling gesture.

Sherlock nods, bends over and takes a few deep breaths. Even a quick chase over blistering hot pavement and soft, sticky asphalt took more out of him than he expected, and his shirt is soaked through. John is breathing deeply, but other than a flushed face shows no outward sign of being overheated.

A few deep pulls from a cold bottle of water and Sherlock feels more or less himself, and when the haze of heat and exertion lifts, Lestrade is chatting amiably with John and holding a bottle of water to his cheek.

"—well, a 60 pound pack plus weapon, and it gets just roasting in the south. Mountains weren't too bad, though. But once I turned in my weapon and decided to join the RAMC full time they sent me to Qurya. Brutal." John smiles, a lopsided grin that crinkles the skin around his eyes and makes him always look so wry, so knowing. Sherlock forgets what he did before, sometimes. "You okay, Sherlock?" John asks, and Sherlock blinks, looks down at John's hand suddenly wrapped around his wrist, taking his pulse.

"Yes," he says, and shakes John's doctorly grip from his hand.

John eyes him skeptically. "You're a bit overheated. Drink that water, and you could at least wear a short sleeve shirt. You're going to keel over."

Lestrade snorts a laugh at that and mops the back of his neck. "You should have seen him last summer, Thought he was going to drown standing still."

"Hmph," Sherlock says, wraps himself in as much dignity as his sweat-soaked clothes will allow and stalks off.

The heat is unrelenting, and Sherlock takes to sleeping on the sofa, draping it with a sheet to keep his skin from sticking to the leather. He spends the first night tossing and turning, his legs tangled in sweaty pajama bottoms even as his bare shoulders soak damp patches into the sheet. The fan almost sucks in more hot air than it dispels from the close, humid room, and Sherlock is miserable and staring at the ceiling at 5AM, watching the first hint of another miserably hot dawn break across the sky.

John must be naturally heat-tolerant, Sherlock supposes, and three years stationed near a desert probably increased his ability to deal with the heat tenfold. But his cool poise in the hottest part of the summer irks Sherlock's stretched nerves in a way he can't define, and in the certainty of a great idea that only comes in the middle of the night Sherlock is determined to make John sweat. Even if just a little, just a tiny, dewy drop.

The next morning Sherlock starts his assault.

It starts with a sneaky reconstruction of the fan – namely, he jams the switch into the off position, and hopes John doesn't look too closely at his handiwork. Windows closed a third of the way to restrict the cross breeze, and a noxious collection of agar plates warming in the oven. The entire thing takes him less than thirty minutes to implement, and when John comes downstairs in shorts and tee shirt a few hours later, Sherlock is placidly reading a book, finally conceding to the heat at least as far as to wear a tee shirt himself.

"Christ, is it hotter in here today? I thought we'd at least get a break in the—oh. Why isn't the fan on?"

Sherlock shrugs, turns a page. Grits his teeth when a drop of sweat lands on it.

"For fuck's sake, Sherlock, now the switch isn't—Jesus, what did you even do to it?" John turns and shoots him a dirty look. "I'd have thought you, of all people, would have at least had enough of a sense of self preservation to leave the damn fan alone, at least."

"I didn't do anything to it," Sherlock protests, ruffled that John assumed so quickly. Well, he had, but still a little presumptuous, anyway.

"You did, and I'm not going to replace it. Melt, for all I care." John reaches for the hem of his tee shirt and strips it over his head in one fluid motion, tossing it down the hall toward the bathroom. "I'm perfectly fine." He walks into the kitchen and pours a large glass of orange juice and sits down in his chair, directly in Sherlock's line of sight.

Sherlock's attention is arrested by the sight of him, only the second time he's seen John without a shirt on. Even a year home he still has tan lines on his biceps and neck, a discoloration of skin from the Afghan sun that will likely last another few years, at least. There's a line across his jaw that is much fainter, but still present, from a helmet's chin strap, and the puckered red wheal of his injury is stark against the creamy skin of his shoulder. He's a picture, sitting there, a country's battleground mapped out in scars and melanin, cool and relaxed and casual as if he were having a picnic on a May day in the park.

Sherlock scowls at him. This isn't working nearly as he'd hoped, the temperature in the flat nearing 29 degrees and he's crawling out of his skin with the stress of it. Heat really does bring out the worst in him. Everything is hot, sticky, uncomfortable, and as he watches John's throat work as he swallows down juice that is so cold condensation is sliding down the glass and down John's forearm, he wants to scream aloud.

The startling realization he wants to lick that cool water from John's skin is really just the melted icing on the cake.

The next day he tries conscripting John to take soil samples in the park ("Now? Well, you better put sun lotion on, you'll burn."), takes him on a false chase after a member of his homeless network ("Honestly, Sherlock, put this cold cloth on your neck, you're going to have heatstroke."), and pulls the both of them into a ridiculously straightforward domestic murder investigation in a tiny flat with hardly any windows ("Wonder how they managed, in the summer. Wait, Sherlock, you can't put your head under the tap in here, it's a crime scene!").

Sherlock admires John, really, his poise and confidence and devil-may-care attitude that is much more in line with himself than he'd expected, coming from such an upright, queen-and-country sort of man. But by the end of the following day he wants to throttle him.

Their hotbox of a flat is almost shimmering, radiant heat from the window glass dancing in waves in front of Sherlock's eyes. The newsreader on the telly cheerfully predicts storms that will break the heat later in the evening or early the next morning, much to Sherlock's relief. John's pulled out his dust-colored singlet and a pair of khaki colored shorts, and living one more day with his smooth, sculpted biceps and perfectly dry skin is going to drive Sherlock mad.

Sherlock takes a cool shower, sprawls out naked across his bed, and waits for John to get back from a last minute trip to Tesco for more cold juice and probably beer. Sherlock hopes he brings back some grapes for the freezer. He ought to text him, but the effort of actually reaching for his phone is too much to contemplate.

Sundown comes, a buildup of clouds apparent in the way the light changes as it filters through his window. The storms that the weatherman told them about are on the way, and Sherlock can feel the stillness in the humid air.

"I brought a new fan," John calls from the hall, and Sherlock jumps, throws on a pair of gym shorts and goes to investigate the purchases. John has the fan set up in the window, a large, box-shaped thing that should at least circulate enough air to make the sitting room bearable. Ha, grapes there are, and Sherlock pops a few into his mouth and puts the rest into the freezer, pausing to stick his face in there for a few seconds. He then watches John slide a few books around the floor in order to get a better angle on the fan, and has an idea.

"You should really move the chairs in line with the fan, so we can both feel maximum airflow."

John turns, looks over his shoulder, and blinks a couple of times as Sherlock eats a few more grapes. "Sure, I suppose," he says, and tugs his chair over and next to Sherlock's, so they're side by side.

He's about to sit down when Sherlock adds, "And if you move those boxes, those right there, you'll improve circulation." He watches avidly as John sighs, lifts and moves box after box until they're stacked on the other side of the room. Not even a hint of wetness on his neck that Sherlock can see. John brushes his hands off on his shorts and Sherlock frantically tries to think of something else. "If you wouldn't mind, I think—"

John rounds on him. "Enough!" he snaps, but he's half-laughing. "It's too hot for this bullshit, and you know it. Stop." He lifts a corner of his mouth in a mocking smile. "I can't help it if you're a bucket of sweat every time you lift a finger, Sherlock, but I'm not your personal servant. Now, if you don't mind, I'm going to watch some of the match, and then I'm going to bed." He sinks down into his chair with a sigh and closes his eyes for a moment, then opens them and says gently, "It'll be cooler tomorrow, Sherlock. You'll feel better then."

Sherlock grumbles and sinks back into the sofa, too disgruntled even able to sit close enough to John to enjoy the fan. John doesn't say a word about it but goes to bed an hour or so later, leaving Sherlock alone in the now quiet, dark room.

The curtains are perfectly still, not a whisper of a breeze, and the heat now has that oppressive, heavy quality that leaves Sherlock buzzing with the anticipation of thunder, of lightning. The leather sofa holds his heat, so he wanders to the window to watch the heavens open up and wash the sultry haze from the sky.

He realizes now that wants to break John, wants to see him finally lose that quiet, collected demeanor and succumb to nature like the rest of the world. Wants to see him glisten, watch his skin go slick and gleaming, to feel if his body gets as hot as Sherlock's own.

He's almost startled when the thunder does come, a crash that jolts the windows and rattles the doors, a swish and flash of rain highlighted by the streetlights. The fury and majesty calls him, so he throws the window wide open, pushes up the screen, and leans out into the storm. The rain cools his flushed face, runs in rivulets down his neck, his bare back, his chest, and he laughs with delight as goosebumps rise across his skin.

"Told you you'd feel better," he hears and he jumps, pulls his head inside and sees John standing in the doorway, one shoulder leaning on the frame and watching him with hooded eyes.

"I could barely think it was so oppressive," he says, acutely aware of the rain dripping from the ends of his hair.

"You haven't acclimated. I still am, but it took a year."

"Is there anything, then, that makes you sweat?" Sherlock asks quietly, and the tension is electric, crackling.

John smiles, molasses-slow and sweet. "A few things."

Raindrops patter on the wood floor from the open window as Sherlock crosses the room, the back of his neck tingling, chest tight with anticipation. John looks up from under his eyelashes as Sherlock leans close enough that a few drops of rain fall from his hair onto John's shoulder.

The taste of the rain licked from John's shoulder is salty-sweet, and his skin is as smooth and warm as Sherlock expected. When he lifts his head John turns, their mouths meeting in a hot, wet kiss that only breaks when the thunder shakes the windows once again.

They stumble down the hall still wrapped in each other, Sherlock trying to kiss John's mouth at the same time John's trying to get a hand on Sherlock's arse, and they drop on the bed still tangled together. Sherlock is more desperate than he wants to be, craving more than he expected, and he can't stop kissing even as John climbs over Sherlock's lap and straddles his hips. Sherlock lifts into him, desperate for any pressure on his growing erection, and he watches with fascination as John's eyelids droop with pleasure.

It's only a quick moment of fumbling before they're both bare, a sweat-slickened eternity of kisses and caresses and gentle fingers until John presses inside Sherlock's body, Sherlock's legs wrapped around John' s hips. Sherlock gasps out his pleasure, the feeling of John fully inside him so intense, his rocking thrusts so perfect Sherlock almost misses the tiny, dewy line of sweat on John's upper lip that catches the flash of lightning from the window.

He watches, fascinated, as it grows, as the ends of John's blonde hair grow dark-tipped and wet, and when John stretches out above him and pins Sherlock's wrists to the bed, a drop of moisture drips from the end of John's nose and lands on Sherlock's chest.

"Finally," Sherlock gasps, and he looks into John's face. He looks almost as wrecked as Sherlock feels, his expression naked, feral. "You look amazing."

"Is that what this is about? Jesus, Sherlock, every time you walked through the room without a shirt on, I wanted to fuck you over the chair, the table, wherever. God, I'd watch the sweat slide down your spine and—" John gasps and his thrusts speed up, rocking Sherlock against the sheets, the slick sound of skin on skin filling the room. Sherlock can feel the moisture building between them, everything slippery and hot, and his cock is sliding against John's belly in a way that has him biting his lip to keep from yelling. He tilts his hips up and tightens down on John's cock, and Sherlock's name is on John's lips as he comes, nose buried in Sherlock's neck and moisture trailing down Sherlock's cheek. It takes only a shivery moment until Sherlock follows him, his orgasm shuddering up from belly to brain and leaving him limp and breathless as the storm continues to howl around them.

The bed is soaked, but Sherlock can barely move when John collapses on his side next to him and puts his head on Sherlock's shoulder.

"We need a shower," he sighs, and kisses Sherlock's chest. "I'm all wet."

"And I plan to keep you just that way," Sherlock says, and kisses the sweet line of sweat from John's upper lip.