While cleaning Lille DIPJ station, Morgane Alvaro, housekeeper, with an IQ of 160, lets drop the file of the murder of Antoine Levasseur, found dead at his home. She can't help reading it and finds out that Jeanne Levasseur, his wife, missing since the day of the murder, is innocent. PJ finds out that Morgane has been messing around with the Levasseur files and Commissaire Hazan, being pressed by her superiors, ask her to help them with the investigation and the disappearance of Jeanne Levasseur. Commandant Karadec is then obliged to collaborate with Alvaro.

A car drives into the forest with two scared girls trapped in the boot. The day after, Florence Grangeon reports the disappearance of Laura and Juliette Sorin, her 5 and 8 year old daughters, to the DIPJ in Lille. She and their father, Franck Sorin, had joint custody of the girls and he apparently is also missing. Arnaud, the grandfather and wealthy owner of a luxury hotel chain, considers Franck a marginal follower of collapsology theories, trying to live on a eco-responsible farm. He is the ideal suspect in their probable kidnapping for his father-in-law.