Detective Inspector Gregory
Ian Hunter
Leopold Dryden
Austin Trevor
Chief Commissioner
Gordon McLeod
Hannen Swaffer
Vernon Bartlett
Eric Dunstan
Gillie Potter
Elisabeth Welch
Eve Becke
Gershom Parkington
Percival Mackey
Joseph Higgins (uncredited)
Ivor Barnard
Joan Dryden
Lilian Oldland
Police Doctor (uncredited)
Cecil Bevan
Foreigner (uncredited)
George De Warfaz
Weisskopf (uncredited)
Howard Douglas
Man on BBC Reception Desk (uncredited)
Arthur Hambling
Detective (uncredited)
Vincent Holman
Peter Ridgwell (uncredited)
Bruce Lester
Wife's Lover on Broadcast (uncredited)
Percy Rhodes
Rodney Fleming
Henry Kendall
Julian Caird
Val Gielgud
Guy Bannister
Peter Haddon
Poppy Levine
Betty Ann Davies
Herbert Evans
Jack Hawkins
Sydney Parsons
Donald Wolfit
Sir Herbert Farquharson
Robert Rendel
Director
Reginald Denham
Novel
Director of Photography
Günther Krampf
Art Direction
R. Holmes Paul
Editor
Reginald Beck
Costume Design
Colin Becke
Adaptation
Basil Mason
Assistant Director
Vincent Permane
Sound Recordist
John Cox
Production Supervisor
Hugh Perceval
Eric Maschwitz
Music Director
Geoffrey Goodheart
Original Music Composer
Ord Hamilton