Joséphine and Iris are two sisters with nothing in common. Introverted Joséphine is a historian who lives in the suburbs, is in debt, and has no social life. Abandoned by her husband, she maintains a difficult relationship with one of her two daughters who does not respect her. The beautiful and exuberant Iris is married to a wealthy lawyer and lives the good life in Paris. One evening during a dinner party, Iris brags about how she is writing a novel. When she gets caught in her lie, she convinces Joséphine to write the book for her, in exchange for the sales revenue which will help her get out of debt. But when the novel turns into a bestseller, jealousy causes rifts between the sisters whose lives are about to change forever. Based on the novel by Katherine Pancol.