The architects Alexandre and Ada Perthuis are a model couple who are in love and expecting another baby. When Ada has to go into hospital to give birth, she entrusts her eldest son, five-year-old Nicolas, to her neighbour Sandra Mollière. Single out of choice, Sandra, who runs a bookshop and is an active member of the feminist ‘Les Hérétiques’ group, decided long ago that she doesn’t want to be a mother. However, the time she spends with Nicolas has a decisive impact on her outlook and she develops an enduring attachment to the little boy and his family. In the months that follow, she strikes up a closer friendship with Alexandre. In the course of their long conversations, she teases and chaffs him whenever the subject of motherhood or relations between the sexes comes up. When Alexandre decides that it is time to seek out a new partner, he turns to dating websites and makes the acquaintance of Alba, a teacher whose gentle beauty and iron will leaves a strong impression on him…