Bruce Edwards as Steve Colt

Virginia Lee as Joyce Winters (as Virginia Lindley)

Carol Forman as Sombra, The Black Widow

Anthony Warde as Nick Ward

Ramsay Ames as Ruth Dayton

I. Stanford Jolley as Dr. Z.V. Jaffa

Dave Anderson as Porter-Spy

Theodore Gottlieb as Hitomu

Virginia Carroll as Dr. Ann Curry

Gene Roth as John M. Walker

Sam Flint as Prof. Henry Weston

LeRoy Mason as Dr. Godfrey

Forrest Taylor as Bradley

Ernie Adams as Blinky

Keith Richards as Michael Burns

George Chesebro as J. Carter

Frank Lackteen as A. Kabob

Carey Loftin as Spike

Ted Mapes as Slade

Jack O'Shea as Finnegan

Gil Perkins as Burke

John Phillips as District Attorney Mark

Stanley Price as Filmore Hagen

Larry Steers as Dr. Harcourt

Ken Terrell as Mendoza