Laurence Harvey stars as Sergeant Raymond Shaw, whose U.S. army unit is captured while fighting in Korea, taken to Manchuria, and brainwashed by Chinese communists. The men return to the U.S. with no conscious memory of their experience, and Shaw is awarded the Congressional Medal of Honor for bravery. But when Captain Bennett Marco (Frank Sinatra) starts having nightmares, he begins an authorized investigation into what happened in Manchuria and eventually reveals that the sergeant's brainwashing has transformed him into an unconscious assassin who can be triggered by his communist controllers at will.