During World War II, German Robert Crain (Marlon Brando) goes AWOL and heads to India to live peacefully. He is discovered, however, by the British Secret Service, who force him to go on an undercover mission on their behalf. He is sent to pose as a Nazi officer on a German ship, but Capt. Mueller (Yul Brynner) is immediately suspicious of his new recruit. As Crain realizes he could be found out at any moment, he incites a riot in an effort to gain control of the boat.