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.