A beautiful young woman is trained by a maestro to be an opera star while they try to avoid love.
Mary Barrett (Grace Moore) is singing “One Night of Love” on radio in a contest to study under the maestro Giulio Monteverdi (Tullio Carminati), who is listening on a yacht with Lally (Mona Barrie).
Mary is disappointed that she did not win; but she tells her parents she is going to Italy to study. She takes a boat and goes to Milan, where many people are playing musical instruments. She listens to them from her balcony. Muriel (Nydia Westman) asks Mary to do something about the noise, and Mary starts singing. They applaud her and throw food to her. Galuppi (Andres de Segurola) comes in and tells Mary that he has a place for her in an opera; but she learns she does not start until next season. Mary says she has no more money. Muriel advises to ask Bill and suggests she marry him. Bill (Lyle Talbot) comes in and says the landlady Frappazini (Rosemary Glosz) is coming up to collect the rent. Bill offers Mary money to pay the rent, but Mary says no. Galuppi suggests that they sing, and Bill plays piano. The landlady arrives and joins the singing of “Che mi frena.” Galuppi congratulates her and goes out with her. Bill asks Mary what she is going to do. Mary learns a job is open at the Café Roma.
Giovanni (Luis Alberni) comes into the home of Giulio Monteverdi and starts playing piano. Lally comes in, and Giulio tells her that her singing was bad. He complains that she wants to make love during the lessons. Giulio tells her to leave. He tells Giovanni and Angelina (Jessie Ralph) that music and love do not mix. Giulio says he will never take another pupil.
Giulio and Giovanni arrive for dinner at the Café Roma. Mary is serving food and then goes on stage and sings “Ciri-Biri-Bin.” Giulio walks into her dressing-room and says she has a great voice but abominable technique. He tells her to hold a high C and says she is not ugly. He puts his hand on her stomach, and she threatens to have him arrested. He shows her his card, and she is delighted that he is Monteverdi. She says she will work, and he says he will mold her. He says she must live with him, and she declines, suspecting other motives besides teaching. He says he will only accept her under the condition that there will be no love, or he will throw her out. He says she must learn to hate him.
In his home Giulio puts Mary through various exercises. She laughs at Giovanni imitating her neck movements, and Giulio sends him away. Mary says she has been working for six weeks and wants to know when she will start singing. He piles heavy books on her stomach to strengthen her diaphragm. He lays down and shows her how to do it. Angelina says someone is there, and Bill comes in. Mary wants to see him and screams to get Giulio to agree. He gives them five minutes. Giulio and Angelina leave them alone. Mary tells Bill she may murder Giulio. Bill learns she is living there, and she says she is only a machine with a voice. She says Giulio is egotistical, and she hates him. Bill asks her to dream of him, and he asks her to marry him. Giulio comes back, but Bill wants an answer. Giulio gives Bill his hat and has him leave.
Giulio tells Mary he will let her sing in a provincial opera house. They travel. Giovanni tells Giulio that Mary is nervous and has roses for her. Mary is going to make her debut in grand opera. Giulio says she will be great. He tells her to sing to him. He plays piano, and she sings “The Last Rose of Summer.”
They travel, and she performs in various operas. In Vienna she is to sing Carmen. At a restaurant Giulio orders for her. She asks how he will feel if she faints from hunger. Lally comes over and talks to Giulio, who introduces her to Mary. Lally is jealous because Mary is beautiful; but Giulio denies there is love involved. Mary says goodnight and walks away.
In the hotel Mary complains about Giulio to Angelina. Mary gets in bed. She tells Angelina that she has laryngitis. Giulio calls in two doctors who examine her. They say she is normal, but she can hardly speak. Giulio tells the doctor she was angry at him. Giulio realizes the trouble and borrows a pin from Angelina. He goes in and jabs Mary in the side. She suddenly complains in a loud voice; he apologizes to the doctors because she is a silly child. Mary warns Giulio not to go out with Lally. He locks her in the bedroom and says goodnight. Mary goes out the window.
Mary goes to Bill’s apartment and learns he is going to the opera. Mary tells his man that she will be sleeping there tonight.
Giulio tells Lally about Mary, who asks if he is in love with her. He denies it but complains about Lally’s gown and perfume. He leaves her and goes to a hotel.
The next morning Angelina unlocks the door and gets a phone call from Mary, who apologizes and says she is coming back. Angelina says Giulio has not been home at all. Mary says she is not going to sing Carmen and says she will marry Bill, who hears her as he is coming in. He is happy, but she says she was joking. Mary says she will never marry, and she will not sing. She asks Bill to take her out for fun.
Giovanni comes in, and Angelina says Mary is gone. Giulio comes in and learns she is gone. Angelina says she is going to marry Bill. Giulio with Giovanni searches for them.
Mary goes to the opera house and pelts her poster with tomatoes. She and Bill go to an amusement park and go back to his hotel. Giulio is waiting in his room. He forbids Mary to smoke, and she says she is through with opera and will marry Bill, who kisses her. Giulio congratulates them and says goodbye. He says he must leave because of the opera. Mary asks if they will cancel the opera. Giulio says Lally will substitute for her. Mary tells Bill that they paid for her and will hear her sing.
Mary rushes to get into her costume. Giulio is there, and Mary realizes he fooled her. She says she lost her voice again. The overture is heard, and Giulio blocks her from leaving. Angelina goes out, and Mary sits down. Giulio says this will ruin her. He says he warned her not to fall in love and says he should have warned himself. He tells Mary he has fallen in love with her, and he asks her to marry him. A man tells her she goes on in five minutes. She tells Giulio he will be proud of her.
On stage Mary appears as Carmen and sings “Habanera.” She is a success, Giulio introduces her to Mr. Howard of the Metropolitan. Giulio says she is not ready for that, and she agrees to follow Giulio’s advice. Giulio tells Angelina that he is going home to fix a supper. Bill arrives and tells Mary that this is her life; but he does not fit in. She asks him to wish her luck, and he does so.
At home Giulio sends Giovanni out to get parmesan cheese for the rice. Lally comes in, and Giulio asks her to leave. She wants him to call Howard on her behalf. He says will not. She says he will regret that. She sees Angelina and Mary coming in and puts her hands on Giulio. Mary sees them and asks Angelina to get her a bag. Giulio tells Lally to get out. She leaves, and Giulio tries to explain to Mary. She says she has learned from him, but now she is going to Howard.
Mary is to make her debut at the Metropolitan in Madame Butterfly. Mary is rehearsing and is having difficulty following instructions. She walks off the stage. Angelina tells Mary that Giulio could help her. Angelina says that Lally means nothing to him. Mary says it is over.
People attend the Metropolitan in New York. Bill is with women and is nervous. During the overture Mary says she cannot go on. Angelina says she will sing. Mary sees Giulio in the box under the stage, and he encourages her and calms her down. Mary begins singing “Un bel di.” Bill and others applaud. Mary sings the climactic aria, and Giulio is moved to tears.
This drama portrays the sacrifice a performer makes to develop her operatic art. Teacher and student both try to practice without being emotionally involved; but the process of learning draws them closer together. They are both elated by her success, and her boyfriend realizes that she has entered a different world than his.