In the spa town of La Bourboule, a man is found dead of poisoning... His ex-partner, Irène, head doctor of the thermal baths, has a large stock of medical arsenic which could be the murder weapon. She was accused of the murder and placed in police custody. Called to the rescue, her daughter Fanny, a young captain at the Crim' de Paris whom she has not seen for years, will try to clear her mother's name and discover the truth. Between will, love affairs, business interests and revenge, Fanny's investigation will take her much further than she imagined by plunging her into her own family secrets.