In Milan, wealthy Mrs. Claypool has hired Otis B. Driftwood to help her enter society, but he merely helps himself to her money. He does introduce her to opera impresario Herman Gottlieb, however, who convinces her to hire tenor Rudolfo Lassparri for his New York opera company. Lassparri is a cad who beats his dresser Tomasso, and tries to captivate Rosa, a soprano who only loves chorus singer Ricardo Barone. Rosa also has an offer to go to America and is sad to leave Ricardo, until she learns that he is stowing away with Tomasso and his old friend Fiorello, who has a mutilated contract with Driftwood for Ricardo's services. They stay in Driftwood's room, which is crowded with one occupant, but bulges to overflowing as the stowaways, assorted maids, waiters, repairmen, and a woman looking for her Aunt Minnie, wander in. When they dock in New York, the stowaways unsuccessfully pose as a trio of bearded aviators, then hide in Driftwood's hotel to avoid deportation. Meanwhile, although Rosa and Lassparri are set to perform Il Trovatore , Lassparri refuses to sing with her because she rejects his amorous advances. Driftwood, Tomasso and Fiorello have a plan, though, and turn the performance into chaos. Tomasso crosses bows with the conductor, the music to "Take Me Out to the Ball Game" is substituted for the opera's score, and Driftwood sells peanuts in the aisles. When Detective Henderson arrives with the police looking for the stowaways, the stage is a shambles, but the day is saved when Lassparri refuses to perform any longer and Ricardo takes his place, with Rosa by his side.