

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.
Director: Timothy Combe

The Doctor

Jo Grant

Brigadier Lethbridge-Stewart

Captain Mike Yates

Sergeant Benton

The Master

Captain Chin Lee
Prison Governor

Dr. Roland Summers
Professor Kettering