Doctor Who The Visitation by Eric Saward

This excerpt, drawn from the novelization Doctor Who: The Visitation by Eric Saward, focuses on the arrival of the Doctor, Nyssa, Tegan, and Adric in seventeenth-century Earth, specifically near an English manor house where a family has recently been killed by an android. The companions, separated from their time machine, the TARDIS, encounter a highwayman and actor named Richard Mace, who eventually becomes an uneasy ally in their investigation of strange happenings like plague fires and an unnatural meteor explosion. The central conflict involves an escaped Terileptil Leader, a reptilian alien fugitive, who is using the manor house as a base to spread a genetically enhanced plague using infected rats to commit genocide against humanity, forcing the Doctor and his friends to stop the plot before it is too late.