Season 3 follows the fortunes of a young U-boat crew as they engage in the Battle of the Atlantic, are hunted down by an obsessed Royal Navy Commander (Ray Stevenson) and are sent on a dangerous mission to the Southern Hemisphere. Together they form strong personal alliances under the command of Robert Ehrenberg (Franz Dinda).
And yet Ehrenberg's thoughts remain in Kiel, where he has developed feelings for Greta (Elisa Schlott). The young mother is married to a man who is seriously injured and suffering from war neurosis. Also in Kiel, Wilhelm Hoffmann's daughter Hannie (Luise Wolfram) is trapped in a loveless marriage to Commander Albrecht Lessing (Florian Panzner), a bitter, emotionally distant man. Hannie suffers under the tight constraints of her status and the social expectations that go with it. When she meets the charming submarine commander Schulz (Pierre Kiwitt), she is playing with fire.
Meanwhile in the exotic climes of neutral Lisbon where the exiles, spies and criminals of Europe rub shoulders with each other and their enemies, Hagen Forster (Tom Wlaschiha) discovers a lethal plot to steal a fortune in plundered war time gold. These discoveries and aspects of his own history deriving from dark experiences on the Eastern front, lead him to question his own actions and moral path. They also lead him to a shadowy figure caught up in a conspiracy that might change the course of the War - for the better. That man, very much changed by his own shattering experiences, is Klaus Hoffmann (Rick Okon). These two historically based strands come together in an unexpected, thrilling finale.
Wealthy Rollo Treadway (Buster Keaton) suddenly decides to propose to his neighbor across the street, Betsy O'Brien (Kathryn McGuire), and sends his servant to book passage for a honeymoon sea cruise to Honolulu. When Betsy rejects his sudden offer however, he decides to go on the trip anyway, boarding without delay that night. Because the pier number is partially covered, he ends up on the wrong ship, the Navigator, which Betsy's rich father (Frederick Vroom) has just sold to a small country at war. Agents for the other small nation in the conflict decide to set the ship adrift that same night. When Betsy's father checks up on the ship, he is captured and tied up by the saboteurs. Betsy hears his cry for help and boards the ship to look for him, just before it is cut loose. The Navigator drifts out into the Pacific Ocean. The two unwitting passengers eventually find each other. At first, they have great difficulty looking after themselves, but adapt after a few weeks. At one point, they sight a navy ship and hoist a brightly-colored flag, not realizing it signals that the ship is under quarantine. As a result, the other vessel turns away. Finally, the ship grounds itself near an inhabited tropical island and springs a leak. While Rollo dons a deep sea diving suit and submerges to patch the hole, the black natives canoe out and take Betsy captive. When Rollo emerges from the ocean, the natives are scared off, enabling him to rescue Betsy and take her back to the ship. The natives return and try to board the ship. After a fierce struggle, Rollo and Betsy try to escape in a small dinghy. It starts to sink, and the natives swiftly overtake them in their canoes. Just when all seems lost, a navy submarine surfaces right underneath them and they are saved.
