John kisses Sherlock, sweetly, softly, slowly (so slowly), and everything is lovely and humming and slightly golden (why is it golden?), and then he opens his eyes.
Sherlock's freckles are glowing.
Sherlock's freckles are glowing. And that humming is definitely coming from him.
John blinks. Sherlock has his eyes squeezed tightly shut, a furrow between his eyes.
"You're an alien," John states, and Sherlock gives a minute nod, wincing slightly as he does, eyes still shut tight.
John reaches up to touch the luminescent spots on Sherlock's cheeks in awe, then it hits him like a sucker punch to the gut.
He starts laughing. Howling, even. Sherlock's eyes fly open, and he tries to take a step back, but John's clutching his shoulders and so he can't move much. He's stuck staring down at John and something in his chest starts to whir in confusion as John nearly chokes on his own merriment.
"You're - you're actually an alien," he gasps out. "Literally. I would joke about what kind of alien didn't know how to do the dishes. But you - So when I called you Spock -" he has to stop trying to talk, because it's talk or breathe, and tears are coming out of his eyes with the force of his laughter. Sherlock's whirring becomes more pronounced.
John looks up to see his distress and tries to calm himself, letting go of Sherlock's shoulders to pet his arms and sides soothingly, trying to breathe normally and calm the spasms from his diaphragm.
"No, no, it's fine, I just, really." He stares up at Sherlock, whose freckles are now dimmed and a light blue. "Of all the people in the world, I suppose I should have expected you would be the extraterrestrial one."
Sherlock blinks at him. "You had no data set to work with, you shouldn't have expected anything."
John shrugs. "I probably wouldn't have expected it, even with a data set. You're the genius."
Sherlock cracks a smile, but it's small and fragile, and John has to gather him in, holding him tight, and humming into his ear as the confused whirring starts again. He can feel it in his chest, coming from Sherlock's ribcage. After a moment of his determined hugging, Sherlock slowly hugs him back, and John is only partially surprised when four arms encircle his back. He can feel the whirring get stronger, an audible representation of Sherlock's anxiety.
So he pulls back after a moment, not letting go of Sherlock's waist (if that is a waist, he doesn't know alien biology). Sherlock's arms fall immediately, but John just squeezes him a bit tighter, and asks, "So where were we?"
A brilliant snog on the sofa later (and thorough groping, four hands are brilliant), Sherlock is humming and glowing and doesn't even seem to realise that two small antennae are curled up in his hair. John is relaxed, half sprawled over the detective as one set of hands holds him tight and the others stroke soothingly down his spine.
He's half asleep when something occurs to him and he starts to giggle.
"Oh, what is it now," Sherlock snaps, and John's partially glad that he's back to being demanding and absurd, but mostly he's distracted by the thought -
"So if you're an alien, then Mycroft -"
Sherlock groans with a whirring click, head falling back to hit the sofa arm, as John giggles himself to sleep.