Song-and-dance men Scat Sweeney and Hot Lips Barton flee a carnival in Louisiana with the owner's two hundred dollars after setting the carnival ablaze. They escape as stowaways on the Queen of Brazil , a ship bound for Rio de Janiero. Scat saves passenger Lucia Maria de Andrade from throwing herself overboard and falls in love with her. Maria's guardian, Catherine Vail, has been hypnotizing her in order to force her into marrying Catherine's brother, Sherman Mallory, who is after Lucia's considerable estate. Under Catherine's hypnosis, Lucia turns in Scat and Hot Lips to the captain, and they are jailed. She later wakes and arranges with the captain for Scat and Hot Lips to work for their passage as members of the ship's orchestra. Lucia intercepts a radiogram from Sherman to Catherine which states that Lucia must marry him immediately before Catherine's lawyer, Rodrigues, interferes. Lucia explains Catherine's motives to Scat, who, upon their arrival in Rio, smuggles Lucia off the boat in a bass fiddle case. On land, Scat sells the American act of Scat Sweeney and Ginger O'Roark (who is really Lucia) to hotel proprietor Cardoso. Hot Lips appears on trumpet, along with three Brazilian musicians, who pretend to be Americans. After Lucia refuses to marry Sherman, Catherine hypnotizes her and she exposes the Brazilian trio as imposters to Cardoso. Catherine offers Scat and Hot Lips ten thousand dollars to leave Brazil and hypnotizes them into accepting a duel. They awaken in time to avoid killing each other, and Scat finally realizes that Catherine has been hypnotizing Lucia. After Catherine, Sherman and Lucia have left for Catherine's wedding, Rodrigues tells Scat and Hot Lips that Lucia's estate papers are hidden in Catherine's safe. In order to stop the wedding, Scat and Hot Lips must present the papers to the prefeito , who will be performing the ceremony. They successfully steal the papers, but are caught by Tony and Harry, Catherine's henchmen, whom they hypnotize before escaping. Meanwhile, Rodrigues and comedian Jerry Colonna lead the cavalry in a race to the scene, but are too late. Scat and Hot Lips stop the wedding in time and expose Catherine and Sherman's scheme to the prefeito . Back in the United States, Scat visits Lucia and Hot Lips in a hotel suite in Niagara Falls, where Lucia tells Scat that she has loved Hot Lips all along. After he leaves, however, Scat looks through the keyhole and discovers that Hot Lips has hypnotized Lucia.