When a Russian agent is arrested in London, former spy turned private eye John Smith (Robert Horton) is contacted by British Intelligence boss Max (Sebastian Cabot) and asked to participate in a secret operation behind the Iron Curtain. When Smith refuses, his American girlfriend Mary (Jill St. John) is threatened with immediate deportation. Smith reluctantly complies, only to find himself back in the world of espionage in an exchange plot designed to undermine the Russian Secret Service.