Captain Frédéric Caïn has been assigned a new lieutenant: Lucie Delambre. He multiplies his provocations to scare her away. They are investigating the murder of a young woman found burnt to a crisp in her car. A young writer with an unbridled sexuality, she had many conquests and amorous adventures. But she was also very close to a middle-class woman with a well-ordered life.

Cain and Julie are called to a road accident in which the driver has died; a convertible has gone off the road on a ledge and hit a tree.

The police take in an elegant 50-year-old man whose suit is stained with blood. The man can't explain the stains, and for good reason: he appears to be suffering from Alzheimer's disease.

Two cases collide for the investigators. On the one hand, a 40-year-old man, completely naked and visibly confused, reports the death of his "moms".