A man is murdered in a room with no windows and a steel lined door which locks only from the inside.

Bernard Lee
as Superintendent Meredith

David Knight
as Lexman

Francis de Wolff
as Ramon Karadis

Colette Wilde
as Grace

Christine Shaw
as Linda Buckland

Stanley Morgan
as Sergeant Anson

A.J. Brown
as Commissioner of Police

Richard Caldicot
as Fisher

Edmond Bennett
as Manservant

Simon Lack
as Jock