John's hands were moving, constantly moving. He was rubbing them on his jeans; he was fiddling with the tea, with the sugar, with the spoons; he was tapping his fingers to some nervous tempo he didn't know the tune of. His eyes remained fixed on his hands.

He was clearly agitated about what they'd done yesterday, Sherlock knew.

Sherlock had assured him that there was no reason to be. He'd quoted his friend – it's all fine – earning a twitchy smile, and he'd assured John that he hadn't been hurt, and he'd allowed him to check. But it seemed he hadn't been thorough enough in waylaying his doctor's concern.

He stood up, and John's hands stilled.

John remained standing, looking down at his hands. There was a red patch at the back of his neck, right below the hairline. Sherlock had at first assumed that it was a birthmark – of course now that he knew what John was, he knew it was a scar of some kind. But where had it come from?

Look at the facts!

The scar was on the back of his neck. Difficult to perform surgery on one's self, especially there, especially the kind that would leave such a small and unobtrusive scar; someone had done it for him. Not his sister or his parents, unless his father… but no, John had said his father was a businessman by trade, and his mother had been a secretary before Harry was born. So someone else had removed John's tattoo. One of his fellows at St. Barts, perhaps? Seemed likely, judging by the scar – not entirely perfect, but close enough that it could have been done by someone who was being trained as a plastic surgeon. It had been done shortly after John had made his decision to join the military, but before he enlisted. The person had undoubtedly been told that the tattoo was a mistake – which was true, but not on John's part – and probably that it had been obtained while drunk. In reality, of course, John had simply been ensuring that Manticore would not find him while he was protecting his adoptive country, but that was irrelevant to the motivations of the surgeon. Why had he agreed? Obviously not for money, John wasn't particularly well off and neither were his parents, after the Pulse. A friend, then, a close friend, but not close enough that he – or she, it could have been a woman – would expect to know when he'd gotten it. A fellow student, a short-term yet close friend… a lover?

"Sherlock?" said John.

Sherlock idly noticed that he was stroking the scar with his thumb.

"Sorry. I merely-" Sherlock cleared his throat; his voice had been oddly hoarse. "You puzzle me exceedingly, John. Every time I think I know you, you give me a new mystery."

John said nothing, and Sherlock reluctantly backed away.

"If you can't bear to stay here anymore, I'll understand, and Mycroft will help you find somewhere else to live. I… do apologize for taking advantage of you yesterday," Sherlock said.

John turned around, eyes wide with surprise. "Of me?" he said.

Ah. I have missed something.

"Sherlock, I couldn't stop myself! I could have seriously hurt you! You don't even like sex!"

"Who told you that?"

"You did," said John, confusedly. "You said you considered yourself married to your work. Remember?"

"Oh. Well, relationships," Sherlock said with a dismissive gesture. "But that was just sex. And you didn't hurt me, John. In fact, I rather enjoyed myself. And so did you."

"Yes," said John. "Probably more than I should have."

"I'd really like you to stay, John. If you feel you can't, I'd still like to work with you." Sherlock pursed his lips. "If you liked it, and I liked it, then why are you still so angry about it?"

"Because I could have seriously hurt you if you'd fought me," John said. "And I couldn't have stopped myself if you'd said no."

But I said yes, Sherlock thought. I said yes, and I'd say yes again, as often as you needed. Any time you wanted. But Sherlock didn't say anything else on the subject, because he didn't understand John's objections, and he didn't understand his own desire to overcome them.

John sighed. "You're my friend, Sherlock. I don't want to leave."

"Good," said Sherlock. "That's settled, then. Now, to dinner with your sister, and then we'll see if there's anything at all of interest to do."