Louis Hayward
— Philip 'Scotty' Grayson
Dennis O'Keefe
— Daniel F. O'Hara
Louise Allbritton
— Dr. Anastasia 'Toni' Neva
Carl Esmond
— Dr. Ritter von Stolb
Onslow Stevens
— Igor Braun
Raymond Burr
— Krebs
Art Baker
— Dr. Frederick Townsend
Lowell Gilmore
— Dr. William Forrest
Philip Van Zandt
— Anton Radchek
Charles Evans
— Dr. Homer Allen
Frank Ferguson
— Carl Bemish
Reed Hadley
— Narrator (voice)
Ray Teal
— Police Sergeant
William Tannen
— FBI Chemist
Gale Storm
— Voice on Tape Recorder
Arthur Space
— Mr. North
Tamara Shayne
— Mrs. Ecko, the Landlady
Keith Richards
— FBI Agent Miller
Grandon Rhodes
— Adolph Mizner
Steve Pendleton
— Police Detective Gaines
Howard Negley
— Feodore
Jimmy Lloyd
— FBI Agent Alison
Myron Healey
— FBI Agent Thompson
John Hamilton
— G.W. Hunter
Paul Bryar
Fred Coby
Bert Davidson
Marten Lamont
Lee Phelps
