In 1942, a derelict German cargo ship, the Ingo, departs Tokyo headed for Nazi-occupied France, under the command of Captain Mueller (Yul Brynner), a merchant navy officer whose previous record has been marred by drunkenness. British intelligence learns that the ship is carrying a precious cargo of rubber, desperately needed by both sides. The British devise a daring plan to intercept the ship and capture its cargo. Colonel Statter (Trevor Howard) coerces a German expatriate, Robert Crain (Marlon Brando), into impersonating an SS officer named Kyle. Crain/Kyle is placed aboard the Ingo under the guise of travelling to Europe on a secret mission. His true mission is to locate and disarm the scuttling charges in order to prevent the captain from scuttling the ship and its cargo upon interception by the British fleet. Crain's mission is made difficult because Captain Mueller mistrusts him and restricts his movements. However, he enlists the help of first officer Kruse (Martin Benrath), a committed Nazi who wants to ingratiate himself with the SS. When a German admiral visits the ship, he suspects Crain/Kyle and radios Berlin for confirmation of his identity. Crain now has only a few hours to take control of the ship, and tries to foment mutiny among a group of prisoners being held on board. He enlists the aid of a young Jewish prisoner, Esther (Janet Margolin), to convince the other prisoners to revolt.