This suspenseful drama of political intrigue begins when Korean War veteran Sergeant Raymond Shaw (Laurence Harvey) is recommended for the Congressional Medal Of Honor by former Captain Bennett Marco (Frank Sinatra). Marco refers to Shaw as the bravest, most honorable man he has ever known. Marco is troubled by the statement and starts his own investigation to discover if his feelings have any validity. The trail takes him from Washington D.C. to New York. Piece by piece, Marco discovers his Korean unit was captured and brainwashed by the enemy in Korea, but the exact nature of the cranium cleansing is unclear. Marco is soon followed by Chinese and Russian spies. His actions are also monitored by hypocritical politicians who carry out their perverse brand of corruption while hiding behind the American flag. Shaw is traced to the manhattan home of his mother (Angela Lansbury), who happens to be the top Communist agent in the United States. Tension builds as the brain-scrambled mamma's boy dons his medal and travels with rifle in hand to a political rally at Madison Square Garden. Marco's trance is temporarily interrupted when he is propositioned by Rosie (Janet Leigh) at a subway terminal before rushing to stop the gun-toting Shaw. His target is the newly nominated presidential candidate. If successful, his actions would set off a chain of event leading to the Communist takeover of the United States. Sinatra, who invested heavily in the film production, plays his finest dramatic role in years after a series of throw away efforts involving the Rat Pack. In the wake of the JFK assassination the following year, an obviously shaken Sinatra refused to talk about The Manchurian Candidate.