The Terileptils are stuck on Earth during the time of the Plague in England in the past-August 5(rest of story-Sept. 1 to Sept. 2) 1666 AD. They have killed a family at a manor, control villagers to attack the travellers, and plan to spread the disease with more infected rats. The Doctor, Tegan, Nyssa, and Adric meet highway man Richard Mace, who becomes an aide to them. Adric and Tegan are captured by the aliens. Nyssa destroys a robot sent to take the TARDIS with the help of Adric, who escaped. The Doctor stops the Terileptils but in the melee the Great Fire starts.