During the Autumn of 1942, in the unrelenting deep ocean waters, U-boat Captain Ulrich Wrangel and his men are caught in battle with a US Frigate. As U-113 takes a hit and begins to free-fall underwater, the reality of U-boat warfare becomes startlingly clear. In occupied France at the port of La Rochelle, U-612 is ready for its first voyage. As the young crewmen continue preparing the boat, Klaus Hoffmann reports for duty as the new U-boat Captain to Flotilla Chief Gluck. Following in the footsteps of his famous father, Hoffmann is worried that he will be unable to live up to his namesake’s reputation. Elsewhere at the base, Simone Strasser arrives to begin work as a translator for the German Navy. As she becomes familiar with her new role and colleagues, she meets Criminal Inspector Forster of the Gestapo who takes an instant shine to Simone. However, there is someone that Simone is keen to see as soon as possible: her brother, Frank. As the pair reunite, the happiness proves to be short lived. Frank is heading out to sea as a radio controller on the U-boat, and there is something that he must urgently ask of his sister before he leaves. During rushed goodbyes, he relays what little information he can of the favor he needs. What has her brother gotten himself into? As the U-boat departs, Hoffmann and the crew including First Watch Officer Tennstedt become acquainted with their new surroundings. Tennstedt, frustrated that he has been passed over for Hoffmann’s job, is keeping a close eye on the new Captain. With tensions building, how long before the second in command makes his feeling known?