It's 1941. A German submarine, U-330, patrols the stormy waters of the North Atlantic. It is commanded by Siegfried Lorenz, a maverick SS officer who does not believe in the war he is bound by duty and honor to fight in. U-330 receives a triple-encoded message with instructions to collect two prisoners from a vessel located off the Icelandic coast and transport them to the base at Brest. A British submarine commander, Sutherland, and a Norwegian academic, Professor Bjørner Grimstad, are taken onboard.