Not rated. After an encounter with the deadly Mandragora Helix, the Doctor and Sarah Jane land in 15th Century San Martino. In the midst of danger, secrecy and intrigue, they witness the flowering of the Italian Renaissance. However, the Doctor realizes that a third visitor has arrived with him in the TARDIS. It is a force with the power to wipe out human civilization forever. The Doctor has brought it to Earth, and only the Doctor can stop it.