

Scotland Yard detectives attempt to solve a spate of safe robberies across England beginning with clues found at the latest burglary in London. The film is notable for using a police procedural style made popular by Ealing in their 1950 film The Blue Lamp. It is known in the US as The Third Key.

Jack Hawkins
Supt Tom Halliday

John Stratton
Sergeant Ward

Dorothy Alison
Mary Halliday
Michael Brooke
Tony Halliday

Sam Kydd
Police Constable in Information Room

Glyn Houston
Detective Sergeant in 'Q' car

Richard Leech
Nightwatchman / Gilson
Newton Blick
Deputy Commander

Geoffrey Keen
Chief Superintendent Jim Malcolm

Sydney Tafler
Stone

Peter Burton
Creasey

George Rose
Slob

Arthur Rigby
Detective Inspector at Chester

Ralph Truman
Colonel Blenkinsop

Ian Bannen
The Young Workman - Stanley James
Maureen Davis
The Young Workman's Wife - Mrs. James
John Warwick
Detective Inspector at Shipping Office

Joss Ambler
Cashier at Shipping Office
Barry Keegan
Detective Constable in Hospital Ward

Alec McCowen
House Surgeon
Charles Frend
Robert Barr, Janet Green
Released