A novelist attends the trial of a woman accused of killing her 15-month-old daughter by abandoning her to the rising tide on a beach in northern France. But as the trial continues, her own family history, doubts, and fears about motherhood are steadily dislodged as the life story of the accused is gradually revealed.

Brittany, France, 1980s. A group of friends, fed up with the boring country life and eager for excitement, create a radio station.

Mrs. Géquil is an eccentric teacher despised by her colleagues and students. On a stormy night, she is struck by lightning and faints. When she wakes up, she feels different. Will she now be able to keep the powerful and dangerous Mrs. Hyde contained?