Team T.A.R.D.I.S. arrives in a village in 17th century Lancashire that Graham has never heard of in the midst of a series of witch trials where every woman tried is drowned in the ducking stool. Becka Savage, the fanatical local landowner has just killed her own grandmother when they first arrive. Her cousin, Willa Twiston, is attacked by mud when she trying to lay their grandmother to rest. While The Doctor, Graham, and Ryan are talking to Savage, King James arrives and announces that he will help her rid her town of witches. The Doctor, Yaz, and Willa go back to her grandmother's burial site to inspect the mud but Old Mother Twiston's corpse, along with the bodies of all of Savage's victims become reanimated. When King James' guard tries to attack them, they kill him. While the Companions track the corpses, The Doctor gets arrested as a witch and tried by ducking. She gets herself out of the seat and confronts Savage who admits that when she cut down the oldest tree on the hill to make the ducking chair, she became infected with the mud and has been fighting the infection ever since. Surrounded by the corpses, she transforms into a purely mud-driven entity called a Morax. The Morax mob abducts King James in order to infect him as well but The Doctor, Willa, and The Companions reimprison them in the hill and rescue the king.