In a few seconds, the trawler Marie-Morgane sank inexplicably, with all its crew, annihilating the Lenormand family. Last survivor with her daughter, Nolwenn Lenormand is convinced that a maneuvering submarine is responsible for the sinking. Determined to shed light on the drama, she fights so that the investigation is not dismissed. Gilles Pezenec, the gendarme in charge of carrying out the investigations, sees the affair become complicated when a fourth body is discovered on board, unknown to all...