Wyrd Sisters is the second book in the Witches sub-series of Discworld, and the sixth book in the series overall. I’m not super concerned about the other sub-series in this post, though, so we mainly care about the first book, Equal Rites, and Wyrd Sisters itself. We also care about Sourcery, the fifth book in the series overall and the third book in the Rincewind series, mainly because of the implications it has for several of the characters in Equal Rites.
In Equal Rites, Granny Weatherwax helps Esk, the first female wizard, realize her destiny and learn wizardry. Granny Weatherwax is a witch, not a wizard, and in Discworld witches and wizards are very separate schools of magic, one only for women and one only for men. This is the fundamental premise of Equal Rites, although of course Esk upsets everything by becoming a female wizard. At the end of the book, Archchancellor Cutangle of the wizards’ Unseen University asks Granny Weatherwax to be an extracurricular professor for the university, hoping to encourage more women to enter the profession by employing a female professor. The exact details of the arrangement aren’t clear, but the basic idea seems to be that wizarding students will go to Granny Weatherwax for a summer to learn some witchcraft and round out their magical education a bit. It’s the capstone to a sub-plot of Granny Weatherwax and Archchancellor Cutangle putting their differences aside and recognizing what they have in common, mirroring Esk’s own journey in which she waffles between witchcraft and wizardry, always sticking up for the one when a practitioner of the other is talking shit.
Esk (and, for that matter, her friend Simon) is a student at Unseen University as of the end of Equal Rites, third book in the series overall. Then in the fifth book of the series, Sourcery, Unseen University gets obliterated at the center of a new mage war as a sorcerer (an ungodly powerful super-wizard) dissolves the old order of wizards, leading to a free-for-all that leads to an attempted coup against the gods (thwarted not by the gods but by Rincewind, the Disc’s least capable wizard). There is no mention of what happened to Esk. Now, fair enough, Sourcery is not in the Witches’ sub-series, Rincewind has no idea who Esk or Simon are, so he wouldn’t be checking up on them.
Being a book in the Rincewind series, it involves a lot of traveling to exotic locations, encountering fantastical perils, and running away from them at top speed (or, in one case, hitting them with a half-brick in a sock), so there’s not a ton of time spent in Unseen University itself, and most of what we do see directly concerns the sorcerer’s takeover and the disastrous results of the subsequent reordering of the wizarding hierarchy. There’s a lot of talk about how wizards don’t and shouldn’t marry or especially have children (the eighth son of an eighth son is a wizard – the eighth son of a wizard is a sorcerer, and sorcerers are calamitous) and the upper level wizards are all male, but given the recency of Esk’s acceptance into the University and the relative timidity of the integration of female wizards, it’s not surprising that none of them have cracked the upper ranks yet and that they’re still too few in number to be a noticeable presence in the sorcerer’s power struggle. There’s no sign of Archchancellor Cutangle, but the new Archchancellor is said to have been relatively recently appointed, so we can assume that Cutangle bit it at some point to make way for a new character who could more suitably play the role required in the plot of Sourcery. That’s kind of sad, Cutangle was shaping up to be a pretty good Archchancellor despite his flaws, but the plot of Sourcery kind of demanded that the University have a mediocre Archchancellor instead – so it goes.
All well and good for Sourcery, but that does mean Sourcery left Wyrd Sisters on the hook to resolve the fate of Esk (and, implicitly, Simon), because it stars Granny Weatherwax (along with new faces Nanny Ogg and Magrat, the mother and maiden respectively to Granny Weatherwax’s crone). If nothing particularly terrible had happened in Unseen University or Ankh-Morpork (the city the University is built in) then we could assume that Esk is getting along fine while Granny Weatherwax and the other witches are confronted with other troubles off in the Ramtops, far away from Ankh-Morpork. But at last accounting, Esk was at ground zero for the apocalypse! A line about receiving a letter or something would’ve been appreciated, to establish she’s still alive (or alternatively, a line about a funeral to confirm she was a casualty of the war, although that seems like an especially grim fate for a twelve-year old girl who was in the wrong place at the wrong time, and put in a book’s worth of great effort to be there).
It can’t be that Wyrd Sisters is a prequel, either, because it’s a plot point in Equal Rites that Granny Weatherwax doesn’t like to fly on broomsticks and it is a plot point in Wyrd Sisters that she came late to flying on broomsticks but now does it rather a lot. The exact positioning of Sourcery in the timeline is unclear, but I feel like if you’re going to nuke the last known location of your previous book’s protagonists and have readers not worry about it because the Rincewind plot is all set 50 years before the Witches plot (or whatever), then you’ve got to be pretty ham-handed with establishing the timeline, either with explicit lines in the book putting events relative to one another (i.e. “fifty years before the time of Simon there was another sorcerer, a real sorcerer…”) or else by heading each chapter with an actual date.
Discworld is a pretty loose setting which doesn’t generally truck with that kind of timeline finnickiness in the Tolkien tradition. In the first book, Terry Pratchett jokes that you can’t map a sense of humor, and thus kicked Rincewind and Twoflower around to different locations heedless of how exactly they bordered each other, and this is fine. By Wyrd Sisters, we are dimly aware that Ankh-Morpork, Sto Lat, and Lancre are all city states in some kind of proximity to each other, but we don’t really know the details of their international relations with one another, like, we have no idea about the other two city-states’ opinion on the Lancre coup that sets off the plot of Wyrd Sisters, and that’s fine. The books aren’t about these things.
But one whole book in the series was about Esk and Simon and Cutangle, dammit, and if you’re going to start the end of the world from their last known location, some words as to their ultimate fate would’ve been appreciated.