Henry Hathaway's film reveals the workings of the Office of Strategic Services (O.S.S.) during World War 2 and uses original footage of the O.S.S. alongside his own footage. James Cagney is a training officer for the O.S.S who is obsessed with discovering a German traitor within. Whilst completing highly dangerous espionage assignments, he manages to identify the traitor after one of his men is murdered and does everything in his power to root out the murderer.