"Fine," Sherlock repeats with vague suspicion, as though committing it to memory as proof for later, when all of this inevitably goes horrendously wrong and he's the only one who remembers the really relevant details. It's fine. It's fine, and he's ecstatic, really he is.

"I'll be sure to put everything back where I found it," he adds, a joke to take the edge off the rest of it, to bury his own tenuous hope, to cover the steady thudding of his heart. It's not safe, but sod safe. To hell with it and bugger it all.

It is, if he's honest, the last thing he ever wanted after all, and dying young will be quite alright if it's anything like this.

"I'll write mum. You really ought to come; I know how to get out the window at night without anyone hearing, you'll see. We can have all of London if we want it."