Commander Gabrielle Perez hunts for an 11-year-old boy who has vanished from hospital. Elouan had been admitted after developing an eating disorder, but was not yet well enough to leave the hospital. Gabrielle and assistant Alaoui learn that the family history is complicated, and they must investigate quickly, as Elouan's life is at risk. 

Lisa Ferrer, an ambitious young exec at a pharmaceutical company, goes missing after experiencing complicated workplace conflict and mental health problems. Newly appointed judge Leo Etchegarray joins the police team for the search, albeit with the frustrated acquiescence of Commander Amar.

Esther Lewanski is leaving the police, but on her last day becomes worried about Julia, a young mother who has disappeared, abandoning her baby Zoe. Despite the team's and Esther's efforts, Julia can't be found and, at the same time, a girl, Charlie, is found drowned. What's the connection between these two young women?

Small-time dealer Tony is shocked when one of his regulars dies of an overdose after he sells her drugs. Tony needs to cover up his supply trail to make sure his wife and family aren't affected by his criminal behaviour. Pregnant Maya Rosetti convinces her partner Clement to help her solve this conundrum.

A school excursion to Strasbourg Cathedral turns into a tragedy when a teacher is murdered in the cathedral square and nine children disappear. Young commissioner Maya Rosetti doubts her ability to handle a case involving children, so she ropes in her reluctant ex-partner, who's a psychologist used to working with children. The shocked parents pressure the police for answers, but the trail and motivation become increasingly complicated.