Doctor Who: The Mind of Evil

The Doctor and Jo arrive at Stangmoor Prison for a demonstration of the Keller Machine, a device capable of extracting negative emotions from criminal minds.

A prison riot puts Jo in danger while the Doctor assists the Brigadier. Meanwhile, at the World Peace Conference, the Chinese delegate's aid prepares to kill the American delegate.

Newly recovered, the Doctor escapes from his cell with Jo. The Master plans to use the Keller Machine to recruit the rioting inmates at Stangmoor Prison and attack the World Peace Conference.

The mind parasite within the Keller Machine becomes too powerful for the Master to control. It learns how to move on its own and goes on the hunt for new minds.

The Master forms an uneasy alliance with the Doctor so that between them they can subdue the Keller Machine which is now out of control.

The Brigadier brings the prison under control, but the Master has escaped and plans to start a world war. The Keller Machine breaks free of the Doctor's restraining device and the Doctor has no choice but to turn the parasite against the Master.