Colonel Alexei Vlassov (Yul Brynner) is a Soviet spy. In France, he defects. He is whisked to the U.S.A., where Allan Davies (Henry Fonda) takes over the case. After polygraph tests and cross-examinations, Vlassov names several Western European Agents who are also spying for the Soviets. Davies wants to take the listed Agents into custody. Meanwhile, those on the list start dying under mysterious circumstances.