Paris 1900. Sharing a house in the Bohemian District are Roberto, a fledgling Musician, who is composing an Opera with his friend the poet Victor Duval; and the beautiful Cossette, daughter of a retired tenor, who goes up and down the stairs, taking advantage of Roberto's music to train her voice.
The young bohemian musician does not know Cosette, but hears her sing daily. Instead, she's in love with Roberto and follows his steps as a composer.