
150 minutes
3/6/1971
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
as The Doctor

Katy Manning
as Jo Grant

Nicholas Courtney
as Brigadier Lethbridge-Stewart

Richard Franklin
as Captain Mike Yates

John Levene
as Sergeant Benton

Roger Delgado
as The Master

Pik-Sen Lim
as Captain Chin Lee
Raymond Westwell
as Prison Governor

Michael Sheard
as Dr. Roland Summers
Simon Lack
as Professor Kettering
Fernanda Marlowe
as Corporal Bell

Neil McCarthy
as George Patrick Barnham
Clive Scott
as Arthur Linwood
Roy Purcell
as Chief Prison Officer Powers
Eric Mason
as Senior Prison Officer Green
Bill Matthews
as Prison Officer
Barry Wade
as Prison Officer
Dave Carter
as Prison Officer
Martin Gordon
as Prison Officer

William Marlowe
as Mailer
Hayden Jones
as Vosper

Kristopher Kum
as Fu Peng

Tommy Duggan
as Senator Alcott
David Calderisi
as Charlie

Patrick Godfrey
as Major Cosworth
Johnny Barrs
as Fuller
Matthew Walters
as Main Gates Prisoner

Timothy Combe
as Prisoner (uncredited)