When her chronically unemployed husband runs off to start a crocodile farm in Kenya with his mistress, Joséphine Cortès is left in an unhappy state of affairs. The mother of two--confident, beautiful teenage Hortense and shy, babyish Zoé--is forced to maintain a stable family life while making ends meet on her meager salary as a medieval history scholar. Meanwhile, Joséphine's charismatic sister Iris seems to have it all--a wealthy husband, gorgeous looks, and a très chic Paris address--but she dreams of bringing meaning back into her life.

When Iris charms a famous publisher into offering her a lucrative deal for a twelfth-century romance, she offers her sister a deal of her own: Joséphine will write the novel and pocket all the proceeds, but the book will be published under Iris's name. All is well--that is, until the book becomes the literary sensation of the season.