Date: March 6, 1971

Rating: PG-13

Genre: Science Fiction, Drama, Adventure

Length: 2h 30min

User Score: 75%

Description: 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.