Lea Morel celebrates her 17th birthday by attending the local Lyon music festival with her friends, but her failure to return home the next morning sees her desperate parents contact the police.

Lea's father Julien is in police custody for lying about his alibi and refusing to give his actual whereabouts on the night of his daughter's disappearance.

Julien is woken by a frantic message on his mobile phone from Lea asking him to call her. Molina and his team track the call to the train station. Nicolas, a waiter at Morel and Sons restaurant, shows Julien the illegal police radio interceptor he has in his car, and as Julien listens to the communications he begins to shadow their investigations.

Francis Dupuis is interrogated about the murder of Lea Morel, but he is obviously confused and unclear about details despite his confession. However, when the police search his property they make a surprising and convincing discovery.

The waiting is finally over for the distraught Morel family when Lea's body is found in Miribel lake. As they prepare for the funeral, Julien becomes obsessed with identifying everybody who attended her birthday party on the day she went missing, and manages to identify someone who looks out of place in the club.

An apparent suicide with a long confession seemingly concludes the case of Lea's murder, but Molina is not convinced.