In many ways it's a story that's been told a thousand times in the Johnlock corner of the fandom: how the two of them finally got together, what was holding them apart and how that's overcome, and (in the wake of series three) just what the heck do you do about Mary. Don't get me wrong, I'm still looking forward to telling #1,001, my soft spot for this kind of story is nowhere near satisfied if only because the fun seems to really be in working out how those two characters will get together and not just that they will, and I wouldn't have been disappointed if I read this story and that was all there was to it. It's an enjoyable trope, and this particular story was masterfully told.
But what_alchemy goes further, bringing in a really very fascinating twist. In her world, everyone is born with a birthmark, called a heart-seam, where the person they're meant to fall in love with is quite literally etched across their chest. First names only. It sounds storybook in its way, a very explicit version of the idea of soulmates, but it seems to cause as much trouble as it avoids, both for the people who spend their lives looking for someone with the name they were born with and for those folks who decide to marry someone even though it doesn't meet their heart-seam. All of which sets up some really interesting ways to look at free choice, predestination, and all other kinds of things that just set my inner philosopher tingling.
I don't think I'm giving away too much (if you're familiar with the way these stories work) to say that John's heart-seam says William, and Sherlock's, John. So they could be each other's soulmates but it's by no means a done deal – the names are so common, and in any event John doesn't know Sherlock's full name until late in the game. And John is in one of those choice matches when he marries Mary. So you have some characters in some really interesting combinations of rejecting the old superstition that you were meant to be with someone with the name across your heart-seam – which just sets up the really interesting question, what exactly does learning the other person might be your soul-mate change? Sherlock and John and Mary at different places seem quite hostile to the idea that heart-seams mean anything at all, yet they're all definitely affected by it. I loved the complicated way that all played out, and also the ambiguity in whether John and Sherlock are written across each others' heart-seams. I can't really go into why it's so fascinating in its ambiguity without giving the game away, but to say it scratched an intellectual itch is an understatement.
I also was quite taken with the heart-seam case John, Sherlock, and Lestrade work. There's a serial killer who's been killing women named Elizabeth because that's the name on his girlfriend's heart-seam. It's standard jealousy in a way, but the kind of murder that would only occur if he took the heart-seam idea seriously. What struck me (and I honestly don't know if this was a conscious choice on what_alchemy's part or not) is that Elizabeth is Mary's middle name as well.
So we've got John and Sherlock investigating someone who murdered women named Elizabeth because he thought they presented a challenge to his chosen relationship, and then Sherlock has to of course navigate the revelations about Mary's character in HL, and he takes it to the other extreme of being perhaps too forgiving and accommodating for John's own good. It's not an exact parallel, but again it sets up some really interesting ways to think about the whole issue of soul-mates, whether it's a good or a bad thing and just what it would change.
I was a bit bothered by the way neither John nor Mary (and especially Mary) seemed overly committed to commitment. This is hardly a problem unique to this story, but there is a sense, I think, that John's and Mary's marriage can be dissolved without any real problem, particularly if they both agree to the break-up. That seems to be the predominant idea in a lot of peoples' thought these days, that things like sex and marriage aren't intrinsically right or wrong but that morality in such things comes down to everyone's consenting. So there's a question of how divorce can be wrong if both parties are on board with it and if no one else is hurt, but I've never been convinced it was quite that simple. Divorce may be the best of all bad options, and in some cases it's definitely better than staying in a bad marriage, but still, there's a part of me wanting to insist that there's still something about divorce that needs to be taken into account here. Breaking a vow, even where both parties agree to set the vow aside, seems like the kind of thing that isn't morally neutral, it needs to be factored in and overcome. And in a story that's all about free choice and the things that limit them, this seemed like it could have been really interesting to look at in a more substantive way. For John or Mary or both of them to work out why this vow could be set aside, why it was proper for John to be with his soul-mate (or why it was proper to be with Sherlock for some other reason) and how his freely-made marriage vow entered into all of that.
As far as faults go, it's hardly a fatal one. It's a short story, after all, and that usually means you have to keep your eye on the prize and only talk about the aspects that are most interesting to you. Plus, this is Mary. What_alchemy is hardly alone in perhaps being at a bit of a loss for how to thread this particular situation. She definitely gave Mary more grace and dignity than a lot of fanfic (indeed, than the show) gives her. It's just an area I'd like to have seen get a bit more attention. But really, if it's a blemish it's a very minor one. The story was thought-provoking and beautifully written, and just ambiguous enough to avoid easy answers. My favorite kind of treat, and I highly recommend it.
(PS: I know some people reading this don't like sexually explicit stories. This one does involve both John/Mary and John/Sherlock, but it's also teen rated. It doesn't get any more explicit than Faramir and Éowyn kissing on the battlements of Minas Tirith, for either couple.)