In the spring of 1943, Lieutenant Ehrenberg prepares submarines for use in Kiel; minors are drafted as crew and Wilhelm Hoffmann attends a reception at the request of his son-in-law.

In Lisbon, Forster investigates the murder of a Gestapo man; the young crew of U-949 experience their first dive.

During a test, the U-949 is in danger due to Commander Buchner's orders; Forster finds a lead in a casino and makes the acquaintance of the German Bettina Gruber.

Ehrenberg saves Pauli and Harri's skin during the tribunal; meanwhile, the tensions between Hannie and Lessing are running high and he humiliates his wife in front of everyone; in Lisbon, Forster discovers that Dr. Beck is an Allied spy.

Forster hands over Dr. Beck, but doubts are rising inside of him; he meets his alibi, Inês, and spends the night with her; in Kiel, Ehrenberg says goodbye to Greta and U-949 sails out; during their first attack on a convoy, a torpedo gets stuck.

Thanks to Pauli and Ehrenberg, U-949 escapes HMS Perseverance's deadly grip; Forster surveilles Gardiner and violently meets Klaus Hoffmann.