When the Tenth Doctor and Donna arrive in ancient Pompeii, it soon dawns on the travellers that a great tragedy is about to happen – Mount Vesuvius is poised to erupt.

When Donna is overheard by a member of the Sibylline sisterhood – a prestigious cult of soothsayers – warning of impending events, she is kidnapped and taken to their temple where she encounters the High Priestess who is slowly turning to stone.

Inside the volcano the Doctor discovers a cavern filled with Pyroviles – creatures composed of rock. These aliens want to conquer the earth after their home planet has been lost.