Having spent her last $500 to study singing in Italy, Mary Barrett takes a job as cigarette girl in a Milan café where her talent is recognized by Giulio Monteverdi, the fiery, egotistical, conductor who is famous throughout Europe. Monteverdi is so impressed that he offers to teach her, making it clear that becoming his pupil will mean years of rigorous training. Told she must live with him so that he can supervise every phase of her life, Mary balks. But with characteristic egotism, Monteverdi assures her their relationship will be strictly platonic, noting that he dismissed his last pupil after she fell in love with him! Two long and demanding years after becoming Monteverdi's pupil, Mary loses her temper with her stern taskmaster. But when he appeals to the artist in her, Mary continues her studies. So, when Bill Huston, a charming and wealthy American, asks her to marry him, she refuses, still determined to become a famous opera singer, if only to gain her stern teacher's approval. Because of their nonstop fighting, Mary comes to believe that she hates Monteverdi. But when he makes a date with Lally, a former student with whom he has had an affair, she tries to keep him home by pretending that she has lost her voice. Wise to the ruse, Monteverdi locks Mary in her room before going to see Lally, only to realize that it's actually Mary whom he loves. Annoyed by Monteverdi's treatment, Mary escapes to be with Bill, telling him she's going to marry him. Hearing the news, Monteverdi pretends to congratulate the couple. But with Mary scheduled for a debut that night, he gets Lally to take her place. Just as Monteverdi expected, Mary shows up to perform, and is furious when she realizes he counted on her doing just that. When she threatens to leave, Monteverdi takes her in his arms and tells her he loves her. That night, Mary is inspired, singing so well that she is offered a role at the New York Metropolitan. But Monteverdi refuses for her - she is not ready just yet. Jealous, Lally manages to convince Mary that Monteverdi made love to her merely to insure that she would sing. Heartbroken, Mary refuses to listen to Monteverdi's explanations and goes to New York to appear at the Met. On the night of her debut, she is so nervous that she cannot go on until she sees Monteverdi in the prompter's box. Recovering to sing gloriously, Mary falls into his arms after Monteverdi pays homage to her as a great artist.