Another adventure for everyone's favourite Time Lord. The Doctor (Jon Pertwee) and Jo (Katy Manning) travel to Stangmoor prison to investigate a machine which can remove evil from the minds of criminals. However, the man behind the scheme - Professor Kellerman - is in fact the Doctor's arch-nemesis, the Master (Roger Delgado), and is planning to disrupt a United Nations peace conference. Inside the Master's machine is an alien parasite which can make people see their greatest fears, and is growing stronger all the time. Can the Doctor stop both the Master and the unearthly parasite?

Three feature-length Doctor Who adventures. In 'Doctor Who and the Silurians' (1970), Jon Pertwee stars as the third Doctor, who is called to an atomic research station in Derbyshire to investigate a series of mysterious events. His questions uncover a vicious ring of in-house saboteurs and something a bit more slimy. In 'The Sea Devils' (1972), after visiting their old enemy the Master (Roger Delgado) in his remote island prison, the Doctor (Pertwee) and Jo learn of several recent accidents at sea, all of which have been accompanied by reported sightings of strange monsters. The Doctor discovers that the creatures responsible are the Sea Devils, acquatic cousins of the Silurians who are out to reclaim the planet Earth from mankind. In 'Warriors of the Deep' (1983), The Doctor (Peter Davison), Tegan and Turlough arrive at an underwater base on an Earth in the future on the brink of Atomic War. Helping to trigger this war are the planet's original inhabitants, the Silurians and the Sea Devils, aided by their killer pantomime horse, the Myrka.