The three zany Marx brothers play havoc with an opera company and manage to replace the egotistical tenor with the young one in love with the soprano.
Mrs. Claypool (Margaret Dumont) pages Otis Driftwood (Groucho Marx) and complains he dined with another woman. Otis claims she reminds him of her more than her. He repeatedly introduces Herman Gottlieb (Sig Ruman) to Mrs. Claypool so that she will invest $200,000 in opera. Rudolpho Lassparri (Walter Woolf King) chases his dresser Tomasso (Harpo Marx) out of his dressingroom. Ricardo Baroni (Allan Jones) tells Rosa Castaldi (Kitty Carlisle) he is in love with her. Fiorello (Chico Marx) tells Ricardo that he sings better than Lassparri and will be his manager. Lassparri gets a summons from Gottlieb, but Tomasso knocks him out with a mallet. Fiorello offers Otis the best tenor in the world for $10, and they tear parts out of their contract. In the end Fiorello says there is no "sanity clause."
Lassparri refuses to sing; but Rosa sings "Alone" from the ship, and Ricardo sings back from the dock. Tomasso kisses the passengers. Otis finds Rosa crying and gives her a love note from Ricardo. Otis lays on Mrs. Claypool's bed and invites her to his room. His trunk almost fills the tiny room. Fiorello and Ricardo come out of the trunk, and Otis finds Tomasso in the drawer asleep. Fiorello demands food, and Otis orders eggs. Two maids come in to make the bed, followed by an engineer, a manicurist, and six more who crowd in before the door opens and they fall out as Mrs. Claypool approaches. Otis wants to marry Mrs. Claypool's eight million and calls Gottlieb a fortune hunter. After eating, Ricardo sings "Cosi Cosa," and people dance. Fiorello plays the piano for the children, and Tomasso plays the harp. Lassparri tells the captain they are stow-aways, and they are put in detention. Tomasso goes out a port-hole, and Otis throws him a rope. Tomasso climbs in a room and cuts off the beards of the three aviators.
Tomasso, Fiorello, and Ricardo impersonate the honored aviators, but police detective Henderson (Robert Emmett O'Connor) calls them phonies. At breakfast Tomasso uses food as make-up. Henderson comes in and searches, while others move the four beds. Ricardo climbs into Rosa's window and then hits Lassparri. Otis learns that Mrs. Claypool fired him, and Gottlieb tells him to get out. He and the other three have a party in Gottlieb's room and demand he let Rosa sing. Otis takes Gottlieb's clothes and sits in his box, making the opening speech. Tomasso disrupts the orchestra, playing baseball with Fiorello. Gottlieb gets knocked out by Tomasso and by Henderson mistakenly. Tomasso and Fiorello go on stage as gypsies; then Gottlieb and Henderson also do so to pursue them. Climbing on the ropes, Tomasso changes the scenery and turns out the lights. Lassparri is gone, and Gottlieb asks Ricardo to sing. He insists on singing with Rosa. Tomasso, Fiorello, and Otis are arrested, but Ricardo has Gottlieb get them released. After Lassparri is booed, Ricardo and Rosa sing an encore while Otis argues about a contract.
This anarchic mayhem with a heart spoofs society's authorities and social conventions. Groucho says and Harpo does what most people may only dare to think. The cleverness makes it top-notch entertainment with biting social satire.