Bill Matthews

Professor Emil Keller has created a machine that can pacify even the most dangerous of criminals. But when the Doctor and Jo arrive at Stangmoor Prison for a demonstration, things start to go horribly wrong - especially when they discover that the Doctor's old enemy the Master is responsible for the machine.

Investigating mysterious power failures and a death at an underground research centre, The Doctor discovers a colony of Silurians - prehistoric, intelligent reptiles who went into hibernation before man evolved. But now they have woken up, and they are prepared to wipe out mankind with a killer plague to get their planet back.