While in London trying to nab several fugitives who stole a million dollars from a U.S. Treasury vault, American federal agent Dennison (Dennis O'Keefe) assists Scotland Yard Insp. McClaren (Philip Friend) in his search for a missing atomic scientist (Paul Hardtmuth). The detective duo discovers that the key to solving both cases may rest with the scientist's daughter (Margaret Sheridan) and her fascinating diamond.
Dennis O'Keefe
as Joe Dennison
Margaret Sheridan
as Marline Miller
Philip Friend
as Insp. McClaren
Alan Wheatley
as Thompson Blake
Francis de Wolff
as Yeo
Eric Berry
as Hunziger
Gudrun Ure
as Sgt. Smith
Seymour Green
as Lascelles
Paul Hardtmuth
as Dr. Eric Miller
Colin Tapley
as Sir Stafford Beach
Michael Balfour
as Hoxie
Cyril Chamberlain
as Castle
