The corpse of a young woman who has been missing for twenty years is found in the Seine. With this macabre discovery, the investigators resume an investigation that has haunted Revel for years: the disappearance of this young woman, twenty years earlier, was one of his first investigations. Their research leads them to Joël, a somewhat "lost" man whom they suspect of having acted with an accomplice, Jean-Christophe Baillard, a brilliant engineer, friend of Joël during their years of study… twenty years more early on, who actually happens to be a dangerous psychopath.

A woman is found dead in her apartment. Her son, just released after serving a prison sentence for the murder of a 15-year-old girl, is the ideal culprit. But during the investigation, Revel and Rousseau learn that the mother, after struggling to prove her son's innocence, had recently changed her point of view. She had opened up to Renaud, the man who had arrested her son, and who also happens to be Revel's former partner in the Versailles criminal squad. The case requires tact and discernment to be clarified ...