Abigail is in shock after Prigent was killed by the explosion of one of the bombs from the First World War that lined the seabed. And Sylvia, his sister-in-law, an environmental activist he had been following, is in a coma. Defying the ban on going out to sea, the scientist returns to the water to understand and record the seismic activity present in the fault off Fécamp.

Diving into the rift, Abigail discovers that an unknown creature haunts the bay of Fécamp, unable to bring herself to abandon her dead child in the fishermen's nets. The town speaks of the presence of a monster in the bay, and Pierre, a sailor, hatches a plan to catch the "monster".