Fracture Mechanics, by kres (AO3)
I should say up front that this story definitely earns its Explicit rating in the sexytiems department. I might even be tempted to call it PWP or erotica, which is by no means a slur in my book but also simultaneously... sort of accurate and also not at all. You'll see what I mean in a minute. Whether that's an enticement or something to make you hesitant, I leave up to you.
The story itself begins with some of my favorite tropes. A consulting detective and his blogger fighting off hypothermia after a midwinter trip into the Thames. John Watson's BAMF quotient as aphrodisiac. Forgotten tea. That kind of thing. Sherlock finds himself increasingly distracted by minutiae and feels the need to "reset," which in the past he's managed through anonymous sex, and this time John agrees to help him out. Not because he's gay or bisexual or even just in love/lust/etc. with Sherlock but because he's a friend and he wants to help Sherlock out.
What really makes this story stand out for me, though, is it doesn't follow that set of tropes to its familiar (if enjoyable) conclusion. Yes, there is sex – quite a bit of it in terms of word count and percentage of story, and really quite well done. But the story somehow stays wonderfully ambiguous. Sherlock is "compromised" in the sense that he's unusually sentimental. He wants to get back to his true self. This is not a prelude to romance, and yet I'm not entirely sure he manages it. I'm not sure he doesn't, either, which is what's almost haunting about this story. It could go either way.
Its only real flaw, to the extent that it's avoidable (and I'm not sure I could have done much better in this department) is when it comes to John Watson. This is very much Sherlock's story, and I can't imagine it working if we understood exactly what John was thinking or feeling throughout it all. That's what makes it work, for me at least – that we're walking the line of mutually using the other – perhaps Sherlock more than John, but there are no real consent issues or anything of that sort – and that only works because we're kept firmly in Sherlock's rather restricted perspective and knowledge-base when it comes to sentiment. At an emotional level that really works, but at a practical level it does border on pulling you out of the story from time to time.
Example: John is supposed to be rather thoroughly heterosexual, but he also clearly knows his way around anal sex, even gay anal sex. (His knowledge of the male anatomy does not feel at all clinical.) It's not that heterosexual couples can't have anal sex, though in the midst of the story I almost forgot that fact, or even that currently-strictly-heterosexual army doctors can't have ever experimented in that area. But it did make me think there was a story to tell there, if not the one Kres was telling, and it made me think Sherlock would find it very interesting. So that's what I was focused on at that point, and I'm not entirely sure I was supposed to. (Though maybe as a distraction it's actually quite a useful one afterall.)
[Side-note: In fairness to Kres, I should note: she picked up on this same issue and wrote a companion piece looking at some of these issues. I've not been able to find it and will add a link when I do.]
As I said, I really don't see how that problem could be avoided, though, aside from maybe writing a completely different companion piece. I would love to see John's perspective on all this, both because of issues like that and my own latent curiosity and also because I think the story would be interesting as a character study for him. But this is hardly a fault (if it is a fault) that I can see an easy way to fix within the story we're told.
Because besides giving some highly enjoyable erotica, I think it's asking a question worth asking if you're going to seriously explore Sherlock's character and his relation to sentiment: is there a context in which sex – even obviously highly enjoyable sex at the physiological level – wouldn't be enough for him. Or put another way: sure, sex can "reset" him and let him get the focus he needs to succeed at the Work, but is that really what he wants or needs?
This story doesn't actually answer that question, but by leaving it unanswered, you're left with the definite impression that a simple "no" would just be insufficient. And a lie. Whether Sherlock will actually take the next step is really up for grabs at this point, which just is a fascinatingly ambiguous place to leave it. Does this make him a smart genius or a fool or scared or what precisely? And is there a next step worth taking, or is all this just the biochemical aftereffects of sex with someone he had a prior connection to? (There's more than one kind of virginity at play in this story.)
Perhaps, as with Janus Cars, the clue's in the name: Fracture Mechanics, indeed.