Hélène de Graf, a wealthy heiress, is found dead in her home in Savoie, on the shores of Lake Bourget. Thomas, her lover, is accused because he visited her shortly before she was discovered dead. He will spend thirteen years in prison. Upon his release, he has only one desire: to unmask the real murderer. Thus begins a veritable manhunt for him, and for us, a mystery: who killed Hélène? Thomas can count on his sister and her husband, an eminent local doctor who has always believed in his innocence, but also on his best friend, none other than his fellow prisoner. But then, who killed Hélène de Graf, and above all, why? Everyone around her is suspected, starting with her husband Alex, his new wife Paola, and even the casino director, Gilles Delprat.