
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)