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British Intelligence agent John Shay suspects that a security leak caused the collapse of British operations in Vienna. He persuades his girl friend Polly, a secretary at Intelligence headquarters, to allow him access to secret files. The information leads Shay to suspect fellow agent Adam Booth (whose wife, Sarah, has been having an affair with him) of being a double agent for the Soviet Union. Although Shay denounces Booth, his superiors refuse to act on what they believe to be groundless charges, and Shay is suspended from his duties for obtaining the confidential files. Nevertheless, he goes to Istanbul to search for more evidence against Booth; while he is investigating, an attempt is made on his life. With conclusive information from British scientist Philip Crawford, who is also involved with Sarah, Shay then murders Booth and finds a plane ticket to Athens in his pocket. Shay boards the plane, accompanied by Sarah, who is unaware of her husband's death. In Athens, where Shay impersonates Booth, they are captured by Soviet agents and held for an exchange for Crawford. Colonel Scott, CIA agent, rescues Shay and Sarah and reveals that Booth was indeed a double agent being used by the British to transmit false information to the Russians.