Two sisters who have nothing in common. Josephine, an historian who specializes in the 18th century and who is challenged by contemporary life, and the outrageously beautiful Iris, who leads the futile life of a wealthy Parisian. 
One evening during a fancy dinner with socialite friends, Iris boasts about writing a novel. Trapped in her own lie, in exchange for money she persuades her sister, who has been dumped by her husband and is swamped by debt, to write the novel, which Iris will claim is her own.
The book's success will change their relationship forever and radically transform their lives.