In 1940, during Italy’s participation in the war, Salvatore Todaro, badly wounded, refuses to leave his submarine and decides to take it through the Strait of Gibraltar with a young crew of submariners from different regions of Italy.
During the journey, "Cappellini" encounters a Belgian cargo ship, and Todaro realizes he must sink it as an enemy vessel. However, he decides not to follow that order and instead saves 26 sailors from the ship, delivering them to shore.
Thus, in the cramped space of a submarine, the most diverse people gather—men who all their lives were told they were enemies, but now they’ll have to coexist, sharing misfortunes, hopes, and supplies.