In this compelling French dramedy set in Paris during the 1920s, Marguerite (Catherine Frot) is a wealthy woman who is madly in love with opera music. She practices singing four to five hours a day and has a large collection of art objects, sets, and costumes. She also has a peacock named Caruso. Her mantra is "Music is all that matters to me." Despite her commitment and yearning to be a great singer, Marguerite is tone-deaf and possesses an untrained voice that sounds like shrieking when she goes for high notes.

In an early scene in the film, Hazel (Christa Theret), a beautiful young woman, arrives at the Dumont estate as a stand-in for another singer in a benefit for war orphans. Two young men, a journalist Lucien (Sylvain Dieuaide) and an avant-garde artist and anarchist named Kyrill (Aubert Fenoy), sneak into the recital. Each of them will have a small but important role in Marguerite's adventure as an operatic diva. Another person who encourages her fantasy is Madelbos (Denis Mpunga), her butler who gathers a large collection of photographs of her. He also carefully and lovingly watches over her by destroying unfavorable reviews of her singing.

Perhaps the most important person in her life is her husband Georges (Andre Marcon) who can't abide her singing. He admits to his mistress that he is embarrassed by Marguerite's performances before a by-invitation-only audience of sycophantic acquaintances and neighbors. That is why, whenever possible, he causes his car to breakdown so he won't have to hear her sing off-key.

Marguerite's hopes for the future are buoyed by a rave review for her performance by the young journalist. He and his buddy create a wild Dadaist show in which Marguerite sings, but this earns her the ire of her rich friends for associating with anarchists and other social critics and outsiders. Despite this setback, she begins preparing for a public Parisian concert by hiring a voice teacher (Michel Fau) who stifles his disgust over her singing in order to make some much needed money.

Writer and director Xavier Giannoli is to be commended for not making this dramedy into a black comedy propelled by an obnoxious portrait of an astonishingly lonely and deluded woman. Instead we feel empathy for Marguerite and her passion for music. The film is inspired by the true story of Florence Foster Jenkins.