Graham: "Well look at it! This ain't the coronation of Elizabeth the first!"
This week marks yet another milestone for the series this season, as "The Witchfinders" is the first episode both written and directed by women since the early 1980s. It's worth noting how many of the significant milestones this season ("Rosa" was the first episode written by a woman of color, "Demons of the Punjab" was the first episode written by man of color) are historical-set adventures, and that these stories are the ones which have been head and shoulders above everything else.
Team TARDIS was supposed to be heading to the coronation of the first Queen Liz, but instead, they turn up on a Sunday for dancing, apple bobbing, and witch hunting. The latter upsets Ryan and Yaz something fierce as Becka Savage (Siobhan Finneran, a.k.a Mrs. O'Brien from Downton Abbey) puts her latest victim on trial for suspected witchcraft. The Doctor insists there must be no interference with the course of historical events, but that resolve goes out the window the second the intended victim, Old Mother Twiston (Tricia Kelly) hits the water. The Doctor is too late to save her, but she does immediately put a stop to her granddaughter Willa Twiston (Tilly Steele, aka Cleary from Victoria) going up for trial next in front of a thwarted crowd.
Team TARDIS present themselves as the head of the Witchfinder authority which means they are taken in by Savage, the landowner of Bilehurst Cragg, who turns out to be completely off her rocker, She's banned horses as creatures of Satan (she had them all shot). Graham has actually done all the Northern England Witch Hunt tours, and this one doesn't exist as far as he's ever heard. Yaz takes off to get more info out of Willa and help with the burial. Meanwhile, back at Becka's house, the Doctor's lecture about the King James Bible is interrupted by King James I of England, aka King James VI of Scotland (played by Alan Cumming).
This week's episode once again grabs the opportunity to remind the audience that time travel really is a white man's pursuit. "Rosa" drove this home with Yaz and Ryan's horror of being in 1955 Alabama. Here it's blatant sexism, as James cannot fathom the Doctor is anything more than an assistant, whose innate female qualities make her worthless as a leader. Graham has to step in and act as protector, while Ryan finds himself on the wrong side of a royal #MeToo-esque moment, as James openly starts coming onto him with discussions of torture.
The Doctor: It's a very flat team structure.
Meanwhile, there is something mystical happening in Lancashire, as Yaz turns up in time to save Willa from being murdered by tentacle-like tree roots. When the Doctor hears about this, she takes it as an opportunity to leave Graham and Ryan to entertain the King while she and Yaz investigate. Turns out Willa's grandmother was the local apothecary, and also she's the woman who raised Becka, giving Savage a much deeper reason for wanting this family eradicated, since they know she wasn't originally highborn.
Graham and Ryan are tasked with trying to keep the witch trials from continuing but neither are much of a match for the King of England. Ryan does a pretty good stall getting James to unburden himself, therapy-style, providing us with a short history of King James I monologue, but it's not nearly enough. This means the group is in the forest to hear Willa scream when the muddy tendrils which attacked her earlier start reanimating the bodies of the women whose lives were taken as witches by Savage. After the zombie women attack and chase them all off, Yaz, Graham, and Ryan head back to figure out why the zombies aren't following. This leaves the Doctor quite alone with Willa, Becka, and the King. When the Doctor starts putting together that Becka knows more than she admits, Savage pulls out the trump card and accuses the Doctor of being a witch herself, and they tie her up to put her on trial.
(We all saw that coming, right?)
The rest of Team TARDIS, unaware of the Doctor's sudden plight, track the zombie horde through the forest, only to discover the whole lot of them head straight to Becka's house and her bedroom, where they seize the axe under her bed. Puzzled as to where the zombies are going, they realize the bell is ringing for another witch dunking. Only the Doctor wouldn't allow a trial... unless. The team is too late, the Doctor goes under the water just as they pull up. But thankfully she doesn't need help, sliding out of her chains Houdini style (yes, he taught her) and exiting the river on the far bank.
Graham: Or else we shall strike down upon thee with great vengeance and furious anger...
King James: Ezekial!
Becka tries to call out the Doctor as a witch for surviving the dunking, but her cries are feeble, especially once the zombie horde arrives and everyone discovers they aren't here to kill Savage but to obey her. She apparently is infected with the same mud that reanimated the bodies. (Old Mother Twiston knew, which is why Becka had her killed.) In the face of others of her kind, the parasite inside Becka takes her over. It introduces itself as one of the "Morax," part of an alien race whose army was buried in the hill on Bilehurst Cragg, in this backwater part of the galaxy, as punishment for war crimes. Becka cutting down a tree on her property unlocked the prison by accident, unleashing them to take over the countryside.
The dunking stool turns out to be made from part of the tree-that-was-really-a-lock, explaining why it zapped Backa earlier. Team TARDIS breaks it up to use as anti-Morax weaponry (aka torches), puts the Doctor back in charge of the team now that King James is captured and not around to protest, adds Willa to their ranks and heads off to save James, even though he doesn't really deserve it.
With the Morax vanquished, James is sworn to secrecy and erases the town from the witch-hunting records, though not before asking Ryan if he wouldn't rather come back to London instead. (Ryan says no.) Willa, on the other hand, decides to head off to become a doctor. No one can argue with that.