No title, story continues directly on from the prompt.
It's summer and Sherlock's swept out of the flat off to annoy Molly at St Bart's or whatever, he's going to be out all day and John's got a day off from the clinic. It's too hot to bother doing anything useful around the flat, Mrs. Hudson's off on some holiday and he's left alone, so John decides to do what normally would first occur to the average 16 year old boy when left home alone: have a nice, drawn-out wank. It's clearly the perfect opportunity, there's no lurking consulting detectives to deduce what he's up to, no landlady to walk in on him naked in the living room trying to survive the warm weather, it's been forever since he got laid, what could possibly go wrong?
Sherlock forgot something at home and comes back unannounced for it, of course :P I'd prefer sexy results, and no crack. Bonus points if John is completely unembarrassed/too swept up in it to care that he's been interrupted.
And they don't say anything and don't break eye contact as John finishes, and then both of them go about like nothing happened as the heat wave stretches on...
...and the weather gets muggier and neither of them have said anything about it but they both keep brushing too close past each other as they move around the flat, skin sliding against sweaty skin since the heat's reduced them both to as little clothing as possible, and everything is normal and fine-just-fine, but the air is like soup in London and the pressure and heat keeps rising...
...and when the weather's at its worst and they're laying around the flat melting from the heat, having gone 'was that did that did we but no what now' for weeks without saying anything to each other about it, with storm clouds grumbling overhead and the sky like a week-old bruise, they catch each other's glances and...
...without a word go up to the sun-baked roof, as the thunder cracks and rolls, sound hitting like a fist to the chest, and they lay flat beside each other, eyes on the sky.
Sherlock is the first to speak. "That time a while back when I came in and you were-"
"Why didn't you stop?"
"Why didn't you look away?"
"Why didn't you?"
John rolls his head toward Sherlock. "I couldn't."
"Neither could I."
"There we have it then."
The sky grumbles and the first fat raindrops smack the rooftop beside their heads, mist rising as they hit.
"What is it that we have?" Sherlock's expression is unreadable as he faces John.
John rolls on his side, reaching over to ghost a hand along Sherlock's jaw, his neck, fingers sliding along skin from the heat-sweat and rain, settling curled under his ear and into his sweat-damp hair, thumb brushing the curve of his ear.
"You tell me," John says, locking eyes with Sherlock and leaning their foreheads together.
The sky finally opens and a welcome rain covers London.
- - -
(that's all there is to that one)