Eight British and American civilians, service members, and United States Merchant Mariners find themselves adrift in a lifeboat after their ships sink in battle with a German U-boat. In the makeshift vessel, Willi Walter Slezak is pulled aboard and quickly becomes a flashpoint for tension. During an intense disagreement, engine room crewman Kovac Hume Cronyn urges that the German be thrown overboard to drown, but the others push back, with radioman Stanley John Hodiak, wealthy industrialist Rittenhouse Henry Hull, and columnist Connie Porter Tallulah Bankhead arguing that he should be allowed to stay. Connie Porter’s thrill at having photographed the battle complicates the dynamics, and her camera is one of the first possessions lost to a sequence of mishaps.
Mrs. Higley Heather Angel, a young British woman, clings to hope even after learning her infant is dead, and she must be restrained to prevent self-harm. As the group struggles to survive, Willi’s true identity as the U-boat captain becomes clear. The survivors attempt to organize their meager rations, plot a course for Bermuda, and forge a fragile, uneasy coexistence. The crisis pushes them to cooperate under strain, notably when they must amputate the leg of their injured companion, Gus Smith Canada Lee.
Kovac takes the lead on rationing, but a storm shifts control, and Willi, who has been concealing a compass and reveals that he speaks English, wrests influence away from him. Gus Smith, having been drinking seawater, becomes delirious and suspects Willi, who is drinking from a hidden flask. Gus tries to warn Stanley, but Stanley is slow to act. While others sleep, Willi pounces, pushing Gus over the side. Gus’s pleas awaken Stanley and the others, but it is too late.
When the lifeboat discovers that Willi does indeed possess a water flask, Joe William Bendix rips it from Willi’s shirt, only for the flask to break. Willi explains a harsh truth about survival: on a U-boat, everyone has food tablets and energy pills, and having a plan is essential. Enraged, all the other survivors except Joe descend on Willi, beat him, and cast him from the boat to his death.
Rittenhouse laments Willi’s ingratitude, muttering, “What do you do with people like that?” No one offers an answer. Stanley then proposes to Alice Mary Anderson, and she accepts, even as their chances of survival look slim. Connie scolds the others for surrendering, then offers her Cartier diamond bracelet as a lure for fishing. A fish bites, but in the ensuing rush for the oars, the fishing line slips overboard and the bracelet is lost.
A signal appears: the lifeboat spots a German supply ship toward which Willi had been steering them. Before a rescue launch can reach them, both ships are sunk by gunfire from a US warship, and a brief, brutal exchange tests the lifeboat’s endurance. Kovac estimates the Allied vessel will arrive in about twenty minutes. Connie worries about her appearance, while Joe hopes his wife is not worried. Rittenhouse studies a photograph of Joe’s family, though he continues to call him “George.”
A frightened, wounded young German seaman is pulled aboard the lifeboat. Rittenhouse immediately calls for his execution, but the others restrain him. The German seaman draws a pistol, but Joe disarms him. The stranger asks in German, “Aren’t you going to kill me?” Kovac counters, “Aren’t you going to kill me? What are you going to do with people like that?” Stanley confesses, “I don’t know, I was thinking of Mrs. Higley and her baby, and Gus.” Connie adds, “Maybe they can answer that.” The film ends on this unresolved moment, implying that the survivors are eventually rescued and returned to American society, leaving the moral question hanging in the air.
