So it’s no secret that I love AUs; my fandom history is littered with them. Specifically, what I love writing (and reading) are canon-divergent AUs, the kind where you change one single detail – one event, one moment – and then follow the butterfly effect through until you end up somewhere that looks very different from what you’d expect.

The thing I love about a really good, meaty canon-divergent AU is the meta-mystery of it. The reader knows how things should go, and the writer drops them into a situation where something different has happened and they don’t know why. The quickest way for me to lose interest in someone else’s AU is if they just explain the change from the very beginning. I love the chills I get as I’m reading this story and we’re meeting beloved characters in familiar settings but it’s all wrong. I love trying to figure out what happened, slowly getting the shape of it in my head, and then finally getting all the details later on. This is why my AUs always tend to be “change one thing and watch the butterfly effect” stories. It turns the whole thing into sort of a detective story from the reader’s point of view, and I love assembling the puzzle pieces, whether as a reader or as a writer.

For example, a fic I never wrote more than a few chapters of: Tempus Furat (Harry Potter AU). It starts on Halloween night, and Sirius Black is walking through the ruins of Godric’s Hollow, and every HP fanfic reader on the planet knows what that means. Except he doesn’t seem all that upset. And when he gets to his destination, it’s not James and Lily’s little cottage, it’s some grand mansion, and although it’s been destroyed, Sirius’s reaction is more like “well fuck” than grief-to-the-point-of-madness. Then the bad guys pop up, but they’re not Death Eaters (even though their numbers include Lucius Malfoy and Bellatrix Black), they’re calling themselves something else (Firewalkers). Sirius is apparently a member of an organisation called the Silver Guard. He escapes via a portkey to Hogwarts, meets McGonagall, and demands to see the headmaster – who turns out to be Tom Riddle, and not Voldemort, a Tom Riddle who’s certainly got a hard edge to him but is in no way the man who became the Dark Lord.

Sirius explains that he was on his way to meet a double-agent, a Firewalker who has agreed to switch sides; he persuades Riddle to help him get away even though Riddle claims absolute neutrality in the conflict between the Silver Guard and the Firewalkers. Sirius makes his rendezvous, meeting up with… no, not Snape, it’s Remus Lupin, with scars across his face (given him by James Potter) and a snarl in his voice and they hate each other and apparently have since school, but Lupin’s decided to turn on the Firewalkers, so Sirius has to work with him.

So this thing had its own plot (sort of, that’s why it never got written – it’s taken me the fifteen years since then to understand my own writing style and how to move a story like this forward without getting stuck on details) about the Firewalkers and their Mysterious Leader planning to attack Muggles, the Silver Guard attempting to stop them, etc. But the real story was the one that the characters themselves weren’t even aware of (well, most of them…) – working out how the hell we ended up in this situation. Why is Riddle not Voldemort? Where did these two new factions come from? Why do Sirius and Remus hate each other, why on Earth would Remus Lupin ever join the bad guys? (Bear in mind that I shipped Sirius/Remus so this was a very deliberate “everything is Very Wrong” plot element.)

I absolutely live for this stuff, for throwing in all these things that make people go “wait, what, HOW, no!” But I also have strong feelings about what makes a good canon-divergent AU, and often it’s not so much about the ways it’s different from canon as the ways it’s similar. One reason plenty of people don’t read AUs at all (whether canon-divergent or the ones that I used to call Elseworlds, i.e. the coffee shop AUs and their cousins) is because it can feel like it’s straying too far from the canon characters and their world. Funnily enough, Elseworlds often have an easier time with that, because authors are usually trying to replicate the canon emotional beats in this new setting.

Canon-divergent AUs can easily get off track, though, if the author becomes too focused on trying to show how Everything Is Different Here, particularly when it comes to characterisation. Now, I am an absolute sucker for specifically the trope where a good person is on the side of evil but I lose interest if that good person has changed so significantly that I no longer recognise them. For full tragedy and angst, I need to be able to see the person they should be and the potential for them to get back to that.

I think that’s the key of it, for me, though it sounds counter-intuitive: a good AU, even one that has wildly broken the canon timeline, should be trying to get back to the same basic outcome as its source material. The characters (at least the sympathetic ones) should be moving back towards their Real Selves from wherever you’ve punted them. If you take too much away from them and don’t allow them to get it back, it’s not a happy ending even if the characters themselves think it is, because we all know how things should be, and this isn’t it. (Conversely, I  am always okay with adding in things that were lost in canon, such as having canonically dead characters survive.)

So going back to Tempus Furat: Sirius and Remus seem to hate each other, but it becomes quickly apparent it’s predicated on hurt of some kind, that something happened at school to drive them apart and they’re both still snarling over it out of emotional self-defence. The conflict between the Silver Guard and the Firewalkers seems like Death Eaters vs Order of the Phoenix under another name, but Sirius and Remus discover that there’s more going on than that, and the leaders of the two factions are connected in some way. A lot of characters who would be dead in canon (e.g. Neville’s parents, James and Lily) are alive. The goal was at the end of the story to be able to have an epilogue showing this universe’s Harry, Ron, and Hermione going off to Hogwarts in ten years’ time, and for it to be not that different from canon. A different history of a different war (but it’s still over), maybe some different faces teaching at Hogwarts, but overall, we’re back where we ought to be, now with bonus living parental figures.

Another example, which I just wrote: in Pray For Us, Icarus (Good Omens AU) I royally fucked up the last 350 years of Crowley’s and Aziraphale’s existence, drastically altering how they interacted with each other and with Armageddon. The first three stories were specifically designed to show off all the ways this world was different and broken, but even then (particularly in Like a Sunless Garden) I was setting things up to make sure I could get them to a happy ending, because I knew that there were some things that could not be lost along the way, or it wouldn’t really be happy. Once I moved on to the “fixing it” part of the series, it was a question of bringing all the strands together so they were ready to be rewoven back into something that looked as much like canon as possible.

So Crowley had to have the Bentley, and it had to be the Bentley, with an equivalent level of love and history behind it. If we got to Happy Ending 2019 and he had no Bentley it would be on some level tragic even if he didn’t know it. Aziraphale had to have the bookshop, and it had to have the same weight of time and history and his relationship with Crowley attached to it. Crowley had to end up back in his own form, with powers and immortality and all his memories. Aziraphale had to be demonstrably able to heal from the trauma of watching him live and die. They had to be together, and be ready to face the future together.

Again, the question I asked myself was: ten years after the end of this story, are they in roughly the same place as we assume they are ten years after canon? In a happy relationship, with a cottage in the country (if in a slightly different location), and immortal lives stretching out in front of them? With the bookshop and the Bentley and good memories of their past together in various forms? With Aziraphale having learned to cast off Heaven’s yoke and Crowley having earned his freedom from Hell?

Other people’s mileage on this may well vary; I expect there are people out there who feel like having an AU end up back on the same track as canon is a cop-out, but this is how I approach it and the kind of AU story I like to read. It feels very much like a puzzle, and I love the meta-narrative that can only exist because the reader is aware of the contrasts and similarities between canon and this divergent timeline. It’s a feeling I’ve never managed to capture in original fiction (historical AUs just don’t do it for me). And I fully intend to just write AUs of my own original stories too, at some point. 🙂