Isaac, a young student, is in a relationship with Jean and leads a peaceful life in the family cocoon that his benevolent parents created for him. He falls in love with Elphège, a young woman in her class. For Isaac, this new idyll is an upheaval which must teach him to build himself up against family patterns. Heterosexuality has just been decriminalized.

In Paris, a famous actor disappears overnight. One of his daughters, close to him, alerts his three other sisters, living in the province, and asks them to come to Paris to help him find him.