In 1950s France, teenage Frederique (Julie Bataille) and her younger sister, Sophie (Candice Lefranc), are enjoying their summer vacation at a seaside villa, cared for by their nanny. Their mother, Lena (Nathalie Baye), drops by with Jean-Claude (Vincent Lindon), a young painter. When the girls’ father, Michel (Richard Berry), shows up and can barely hide his anger, Frederique realizes that her mother is having an affair, and her parents’ marriage may be disintegrating under the summer sun.  Set in the French beach resort of La Baule-les-Pins in the summer of 1958, the plot revisits the theme of divorce and its effects through a narrated in voice-over from the diary of a thirteen-year-old girl, Frederique.