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?

Two classic Doctor Who adventures set on the planet of Peladon, starring Jon Pertwee as the Third Doctor, with Katy Manning as his companion in the first story and Elisabeth Sladen in the second. In the four-parter 'The Curse of Peladon' (1972), the Doctor (Pertwee) finally seems to have escaped his exile to Earth when he manages to transport Jo (Manning) in the Tardis to the planet Peladon. The pair are mistaken for Earth delegates at a conference to decide whether Peladon should join the Galactic Federation, and discover that someone is attempting to use the legendary royal beast of Aggador to trigger off a war. In the six-parter 'The Monster of Peladon' (1974), the Tardis arrives on the Planet of Peladon half a century after the Doctor's first visit. The planet has now become of great tactical importance because of its focal position between warring factions. The Doctor and Sarah (Elisabeth Sladen) have to act as peacekeepers between rival ambassadors and they must also find the truth behind 'the spirit'.