In her prime, Lea de Lonval (MICHELLE PFEIFFER) was unmatched as the courtesan of choice in pre WWI Paris, a vocation that's left her rich, but without true love. Living in a mansion with a large staff including her personal aide, Rose (FRANCES TOMELTY), Lea is contemplating retiring from her line of work, what with now being middle-aged.
In doing so, she'd be joining the ranks of her fellow and now well-to-do colleagues, Marie Laure (IBEN HJEJLE), whom she can't stand, and Madame Peloux (KATHY BATES), with whom she's now friendly. The latter is worried about her spoiled and lazy 19-year-old son, Cheri (RUPERT FRIEND), and asks Lea for her help.
Yet, what begins as a temporary bit of educating him about life and love turns into a six-year relationship. Lea is generally pleased in her mother-lover role with Cheri, but is thrown for a loop when Madame Peloux announces she's arranged for her son to marry Marie Laure's 18-year-old daughter, Edmee (FELICITY JONES).
She knows it's the right thing for him to do, but finds this development and the subsequent marriage a shock to her self-esteem. From that point on, the former long-time lovers find themselves longing for each other, despite the obstacles in their way, including his marriage as well as the vast difference in their ages.