Suspense-packed espionage yarn, approached from a documentary angle, has Nolan as a no-nonsense federal investigator who is sought out by German-American Eythe, a brilliant student. He has been contacted by Nazi spies, he tells Nolan, and asked to work with them. Nolan encourages Eythe to
accept the offer and work as a double agent, reporting all Nazi activities to the FBI. Slowly, Eythe ingratiates himself with several Nazi agents and is assigned, as a technician, to transmit messages to Germany via short-wave radio. He establishes a remote radio hideout and begins sending
messages, really to FBI headquarters, and its operators pass on fake information to Germany....