The British government asks entomologist Frances Gray (Margaret Lockwood) to go behind the Iron Curtain and examine insects that might be used for germ warfare. Grudgingly accepting the job, Frances goes undercover as a tour director and meets American reporter Bill Casey (Dane Clark) in the process. Unfortunately, the chief of police quickly sees through Frances' cover. When her contact is murdered, Frances is taken into custody and harshly questioned, prompting Casey to come to her aid.