Madama Vastra recounts a story from her past to hr wife, Jenny: with a giant asteroid on a collision course with Earth, the Silurian race prepares to hibernate in safety underground. Seeker Va’stra disobeys the instructions of High Judge Acrocan to enter stasis, and instead investigates a series of recent murders. She soon uncovers a plot to kill members of a gang called the Redcrests, using Deinonychuses, savage dinosaur killers influenced by remote-controlled implants.