Laurène comes face to face with a wolf which appears to be guarding a newborn baby hidden in a box. She undertakes to find the baby's parents, followed from afar by the mysterious animal. As everything rapidly becomes complicated, memories from her troubled past resurface.

An amateur caver emerges traumatised from a labyrinth of subterranean grottos where he says he lost his friend. Laurène tries to unravel fact from fiction in his witness statement before contemplating a perilous descent. At the same time, Cora thinks that the Mayor's daughter has been kidnapped by a mysterious group of activists who are leaving their marks on the walls of Villefranche.

A phone is found with videos showing a group of young people terrified by a macabre discovery in the forest. After the body of one of the young people is found, Laurène and her team investigate, endeavouring to understand what went wrong on their nocturnal spree. At the same time, she tries to assess her complicated relationship with Bertrand, the town's Mayor.