Sherlock slithers onto the living room sofa, feet bare, eyes vacant, flicking his dressing gown up over his knees. Looking across at him, John sees what he expects by now: a beige nicotine patch peeking out from beneath his sleeve.
It occurs to him, as it has many times over his first fortnight at Baker Street, that he's never seen Sherlock actually putting a patch on.
And even three patches wouldn't give you that much of a buzz.
John gets up, slapping the newspaper down on the arm of his chair and not at all surprised when Sherlock doesn't even blink. Nor does he seem to realise what John is up to, until he's crossed the floor and ripped the patch off his wrist.
Sherlock yelps, affronted, and tucks his hand under the other elbow. But it's too late. John yanks it back out again, turning his hand palm-side up and surveying the new syringe prick and faded, bluish scribbles on the inside of his arm.
"Yep," he says. "I bloody thought that's what the patches were for. Where's the rest of it?"
"Where's the rest of what?" Sherlock demands peevishly, pulling his arm back and rubbing his pink, stinging wrist.
"Whatever it is you're shooting up. Go and get it. Jesus Christ, Sherlock!"
Sherlock sits up, a little unsteadily. More than anything, he seems hurt.
"I can't live here when you've got drugs in the flat," John continues, calmly but with a little tremor underneath. An adapted kind of parade rest, arms folded, as he tries to decide how to react.
Sherlock looks up at him sulkily, waiting out the lecture. It takes John by surprise a bit—Harry always gives him hell when he catches her out booze-handed. "I could lose my medical license for this," he says. "And we could both go to prison. Get whatever you're hiding right now, or I'm going to find it myself."
"Lestrade couldn't," Sherlock says, smirking in a way that clenches John's right fist.
"Your brother could, I bet. How about I ring him up and ask?"
It's only when John actually picks up the landline handset from beside his chair that Sherlock gets to his feet and disappears down the corridor.
John doesn't follow. He waits until Sherlock emerges again with what seems like an entire bloody pharmacy full of syringes and vials and powders and pills.
"Right." John surveys the stash and swallows more anger. Has this idiot got any idea what street drugs do to people? "Now you're going to destroy this stuff. All of it."
"Or what?" Sherlock snarls back.
"Or I'm packing up right now and moving out this afternoon."
Sherlock looks at him, astonished, trying to decide if he really means it. "But I need it," he finally mumbles into his palms.
"Then keep it," John says with a shrug. "But I can't live with you, Sherlock. Not when you're like this. Not when you're shooting up in the flat."
The hypodermics end up in John's medical kit. It takes Sherlock half an hour in the bathroom to bring himself to flush the rest.