On his birthday, Meyer receives a curious gift: a wooden sculpture of a devil with a demonic and mischievous appearance. Meyer smiles, recognizing it as a typical art object from Bessans, a village in Savoie. He calls Constance, certain that she sent him the devil for his birthday. But he's in for a nasty surprise: not only did Constance not know it was his birthday, but she's also dealing with a frozen corpse found on the French side of the border, locked in an isolated chapel in the mountains. In the victim's backpack is a carved wooden devil. It's not a murder per se, but how can anyone be sure? Did the victim lock himself in by accident, or did the door close and then jam shut after a gust of wind? Having received the same devil, Meyer decides to get involved in the investigation...

The body of Maude Gaillard, 52, a well-liked psychologist, is found dead in the grounds of a luxury hotel. Suspicion quickly falls on Ida Malapeyre, an unstable patient under judicial supervision whose connection to the victim may be more complex than it appears... As Cassandre's team investigates this lead, the investigation takes an unexpected turn: Cassandre is kidnapped! To save her and uncover the truth, the team must unravel a past that some were willing to kill to erase.