Not less than 3 men and 40 animals were found dead on the Breton beaches. The identity of the killer is an open secret: green algae. Inès Léraud is still a young journalist when, driven by an ecological conscience, she decides to go to Brittany to investigate this phenomenon. Through her encounters with whistleblowers, scientists, farmers and politicians, she elucidates, not without difficulty, half a century of silence: samples that disappear in laboratories, bodies buried before being autopsied, influence games, pressure... Will the truth win?