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.
as The Doctor
as Jo Grant
as Brigadier Lethbridge-Stewart
as Captain Mike Yates
as Sergeant Benton
as The Master
as Captain Chin Lee
as Prison Governor
as Dr. Roland Summers
as Professor Kettering
as Corporal Bell
as George Patrick Barnham
as Arthur Linwood
as Chief Prison Officer Powers
as Senior Prison Officer Green
as Prison Officer
as Prison Officer
as Prison Officer
as Prison Officer
as Mailer
as Vosper
as Fu Peng
as Senator Alcott
as Charlie
as Major Cosworth
as Fuller
as Main Gates Prisoner
as Prisoner (uncredited)
