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.
Jon Pertwee
Katy Manning
Nicholas Courtney
Richard Franklin
John Levene
Score: 7.3
Score: 8.1
Score: 6.2
Score: 0.0
Score: 6.8
Score: 1.2
Score: 5.3
Score: 5.2
