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: 6.4
Score: 6.9
Score: 7.0
Score: 6.0
Score: 2.0
Score: 4.7
Score: 7.0
Score: 7.0
