Hidden in a bathroom cabinet, a small boy watches his mother get brutally murdered before his very eyes. Diane understands that from where he was, the child saw the face of the killer. But little Louis is so deeply traumatized that he isn't able to talk - In his nightmares, the killer takes the form of a vicious wolf, chasing him. Who is hidden behind the wolf that haunts the child's nights? Suspicions focus on Marion, Louis' "second mother", Claire's partner - Meanwhile, Diane's personal life is far from simple. Under Marie-Laure's influence, Zoe has decided to become a medical examiner.