He shouldn't want it but he does.

He watches the man slowly exhale the smoke from his lungs, and then take another pull from the cigarette. The fag. An American once told him that "fag" was a derogatory word for a gay man in Colonial English.

How ironic.

The man tosses away the still-lit cigarette like an old lover, and Sherlock finds himself wanting to pick the discarded cig from the pavement and suck in every last molecule of toxicity he can from it. He wants it, oh god, he wants it, because John is drunk, he is drunk, they're outside a club—a gay club, John so helpfully pointed out—and John is getting married.

John is getting married.

He shouldn't want that cigarette, but he does.

When John laughingly suggests that they go into this club—"for a lark," John says—Sherlock can't say no. Well, he technically could because he is physically capable of forming the word no with his lips, pressing his tongue against the alveolar ridge, and pronouncing the oral vowel, but in the end, Sherlock doesn't say no because he doesn't want to.

Similarly, when they're in the gay club, Sherlock realizes he may have overestimated how much alcohol he can actually imbibe, and John puts his arm around Sherlock's shoulder and introduces him as "his best mate," Sherlock could very easily lead John into the men's room, press his former flatmate against the hideous cerulean tiling that is sure to be in there, and pull the air from John's lungs the way that smoker pulled from that cigarette. He could press himself against John's smaller-but-stockier body in a way he knows the doctor will enjoy. He imagines running his hands under John's jumper, touching abdominals, pectorals, and oh so many other wonderful features of the human body. He wonders if John will touch back, if John wants to explore just as much as he does, if John will press against him just there.

Would John be opposed to getting off in a nightclub toilet?

There's a special room in Sherlock's mind palace-one that overlooks a garden where he and John once investigated the robbery of a topiary shaped like a teacup—where Sherlock goes sometimes to imagine John's reactions to sexual situations. Namely, situations involving him and John. It began as curiosity of the human condition, and ended with him picturing John naked and writhing beneath him, breathing out, "Oh, Sherlock."

He goes to that room now, and thinks of John pressed against the wall of the toilets, trembling with anticipation. Would John push him away if he undid his trousers? Would he say, "No, Sherlock, not here. Not now." He's getting married. This is no time to think of Mary, so Sherlock distracts him with his tongue, tasting John as if for the first time. For John, it would be. For Sherlock, there is a room in his mind palace in which he's catalogued every possible sensory experience relating to Doctor John Watson. Sherlock would use this distraction to undo John's trousers, and to run the palm of his hand against the length of John's erection. "Let me," Sherlock says to this John, "Let me."

Would John say "yes" or would he simply moan his agreement?

It wouldn't matter to Sherlock, so long as he could take John into his hand, and the feel of Sherlock's bare skin on John would nearly undo the consulting detective. But this wouldn't be about Sherlock. If he could ignore his transport for the entirety of a case, he could ignore his urges now too. This would be about John, his John.

"Sherlock, please," John moans, "Bloody move."

And so Sherlock would, slowly at first. Even in his mind palace Sherlock doesn't know if this is a one-off or if it's just another evolution of their strangers-to flatmates-to friends-to partners relationship. He would make this entirely about John, because this is about John, as is almost everything in his life now. As John's breathing would quicken, so would Sherlock's hand, and Sherlock pictures John's face as Sherlock brought him to the edge of release. Would John's eyes be closed? Or would he look at Sherlock the whole time?

Sherlock hopes that John would look at him, that John would see him and know that it was Sherlock Holmes who was doing this to him, driving him to the edge, making him come in his hand. There would be a whole room needed to catalogue John's physical reactions to getting off in a public toilet with Sherlock Holmes' hand wrapped around his cock. He hopes that, afterward, John will rest his head on Sherlock's bony shoulder and mutter, "Need a fucking cig after that."

Leaving his mind palace, Sherlock knows could lead John to the toilets and let alcohol and human urges do the rest, but he doesn't.

What really happens is that he and John drink, he gets in an argument with another drunk patron about the 240 different types of tobacco ash—there are distinct differences, he tell John yet again—and he and John end up outside the club again. This time, it's John with the cigarette, taking long pulls and blowing out spirals of smoke that Sherlock wishes he could live in. He swears to never smoke again, never want to again, if John would just reach over right now and share that latest inhale with Sherlock's lungs.

"C'mon," John says, "Plenty more pubs, yeah?" He flicks the cigarette into the street.

Sherlock stares after it, his drunken brain fixating on the dying embers.

He shouldn't want it, but he does.