It is August 1943 and Franz Buchner is in action with U-949 while an informer on board divides his crew; the Hoffmann family gathers in Berlin to attend the premiere of a film about Klaus.
Robert Ehrenberg supports the resistance movement within the navy and gives Klaus Hoffmann a clue; Bobby Schulz is on his trail; U-949 comes under fire in the Strait of Gibraltar.
Klaus Hoffmann commands the ailing U-330 on a secret dive, but not all the men trust him; Hannie wants to take Hertha in; staff officer Heinrich Gluck has to make a decision.
After a risky manoeuvre, the U-330 shows up next to a US Navy ship; SS man Koch uncovers the identity of the spy Fidelio; Hannie gets on the trail of the Lebensborn organisation.
