Investigating the murder of a street artist, Cannes detective Camille Delmasse keeps running into the suave but shady Harry King. Meanwhile, Camille's father, the former chief of police, is set to be cleared of corruption until secrets upend events.

When a casino owner's wife is poisoned, suspicions fall on blacklisted gambler Roxie Roland. Camille turns to Harry for help, for who better to bring down a con woman than a con man. Harry discovers the name of the man threatening Camille's father.

A monk is found murdered below an island fort; Camille and her partner, Lea, delve into the victim's dark past for answers, with input from Harry's old friend, who was the monk's mentor; a ruthless fixer named Julien Boire threatens Camille's sister.

Camille goes to see her father in prison despite efforts to intimidate her. Ordered to protect a visiting billionaire who has had death threats made against him, she and Lea turn to Harry for intel about a legendary assassin known as the Nightshade.

When Pascal Fontaine is found hanged after a séance, it seems he's the victim of a curse related to the family matriarch's death in a mental asylum; the team deal with shady mediums and scorned lovers, while Harry and Camille set a trap for Boire.

The death of an actress's assistant during the Cannes Film Festival could be an accident or murder, and the case affects Lea deeply; with his daughter at risk, Harry decides to stop Boire once and for all, but what he learns will devastate Camille.