Professor James Bower, an American physicist, is effectively blackmailed by a shady CIA agent named Adams (Roddy McDowall) to help the CIA obtain secret microfilm from a defecting Russian scientist. The reluctant Bower travels to East Germany undercover as an antiques collector where he encounters an East German secret agent named Peter Heinzmann (German actor Hardy Kruger), who is also a fellow physicist. Heinzmann is aware of Bower's meeting with Adams and his intention to steal the microfilm, however their mutual respect for one another's tactics complicate the proceedings.