In this drama film set in World War II, an inexperienced U-shaped submarine team takes on a secret mission, struggling between the deep sea and life and death; at the same time, a young German woman is trapped in the tear of emotions and faith - on the one hand, she has an inextricable loyalty to her motherland, and on the other hand, she is deeply touched by the ideals and courage of the French resistance organization.Loyalty and conscience, responsibility and love are intertwined in the war to form a moving test of human nature.