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.

• DirectorTimothy Combe
• Release6 March 1971
• Genre
  Science Fiction / Drama
• Duration2h 30m
• Budget?
• Revenue?
• Rate
  

  7.5
  10 reviews
• Productions

  BBC