Ian Hunter as Detective Inspector Gregory

Austin Trevor as Leopold Dryden

Lilian Oldland as Joan Dryden

Henry Kendall as Rodney Fleming

Val Gielgud as Julian Caird

Peter Haddon as Guy Bannister

Betty Ann Davies as Poppy Levine

Jack Hawkins as Herbert Evans

Donald Wolfit as Sydney Parsons

Robert Rendel as Sir Herbert Farquharson

Gordon McLeod as Chief Commissioner

Hannen Swaffer as Hannen Swaffer

Vernon Bartlett as Vernon Bartlett

Eric Dunstan as Eric Dunstan

Gillie Potter as Gillie Potter

Elisabeth Welch as Elisabeth Welch

Eve Becke as Eve Becke

Gershom Parkington as Gershom Parkington

Percival Mackey as Percival Mackey

Ivor Barnard as Joseph Higgins (uncredited)

Cecil Bevan as Police Doctor (uncredited)

George De Warfaz as Foreigner (uncredited)

Howard Douglas as Weisskopf (uncredited)

Arthur Hambling as Man on BBC Reception Desk (uncredited)

Vincent Holman as Detective (uncredited)

Bruce Lester as Peter Ridgwell (uncredited)

Percy Rhodes as Wife's Lover on Broadcast (uncredited)