In an ornithological reserve, Mongeville and Valentine discover the corpse of a man pierced by an arrow. While interviewing Béatrice Lesparre, a brilliant and eccentric researcher who lives in the reserve, they soon discover that Claire, the scientist's daughter, has also disappeared. Was she killed too? Is she the murderess? This will be an opportunity for the judge and the captain to penetrate further into this strange matriarchy of a fifty-year-old mother, who seems to protect her 25-year-old daughters as if they were 12...
