In 1942, a weathered German cargo vessel named the Ingo departs from Tokyo, bound for Nazi-occupied France. It's under the command of Captain Mueller, a merchant navy officer with a tarnished past marked by bouts of drunkenness. British intelligence catches wind of the ship's valuable cargo: rubber, a precious commodity desperately sought by both sides. In response, the British hatch an audacious scheme to intercept the vessel and seize its cargo.
Colonel Statter coerces a German expatriate, Robert Crain, into assuming the identity of an SS officer named Kyle. Crain/Kyle is planted aboard the Ingo, posing as someone on a covert European mission. His true objective is to locate and disarm the scuttling charges, preventing Captain Mueller from sinking the ship and its cargo when confronted by the British fleet.
Crain's mission becomes exceptionally challenging as Captain Mueller remains suspicious and restricts his movements. Nevertheless, he gains the assistance of the ship's first officer, Kruse, an ardent Nazi keen on ingratiating himself with the SS. Trouble brews when a visiting German admiral becomes wary of Crain/Kyle and contacts Berlin to confirm his identity. With only a few hours at his disposal, Crain must take control of the ship and seeks the aid of a group of prisoners held on board. He enlists the support of a young Jewish detainee named Esther to rally the prisoners and incite a revolt.
