An inexperienced U-boat crew are plunged into a perilous secret mission, while new translator Simone starts work at the base.

Tennstedt and Hoffmann continue to butt heads aboard U-612, while rebel Carla Monroe plans a mission in La Rochelle.

The U-boat crew struggle with recent events and what lies ahead. A revelation in La Rochelle infuriates Forster spelling bad news for Simone.