When jewel thieves Morton Harding and Rollins hear Italian immigrant Nino Maretti singing on a Hollywood-bound bus, they plot to use him as part of their scheme to rob motion picture director William Goodwin. By pretending to be talent scouts, Harding and Rollins convince Nino to perform unannounced at the wedding reception of Goodwin's daughter, where a valuable pearl necklace is on display. During Nino's stunning solo, which draws the opera-loving Detective Flugelman away from his watch, Harding and Rollins steal the necklace then, with Nino in tow, flee. After the theft is reported, District Attorney Robinson questions Jean Clemens, an aspiring operetta composer who had "crashed" the Goodwin wedding to meet famous conductor Leon Rodowsky. At the same time, Nino, who has been warned to keep quiet by the crooks, shows up at the police station, but is scared off when he realizes that he is the police's only suspect. As he leaves the station, Nino meets Jean and tells her that he is a music promoter whose most valuable possession has been stolen. After enjoying a romantic evening with Nino, Jean finds him a job as an extra for a movie musical that is being directed by Rodowsky. Because Rodowsky has been called on repeatedly by Robinson to identify the mystery tenor's voice, Nino, fearing for his life, remains mute. Later, however, Jean hears Nino singing one of her songs and, hurt by his apparent deception, angrily rejects him. As an apology, Nino turns himself in to collect Goodwin's $25,000 reward, which he tells Jean's roommate Nora to use to finance Jean's operetta. Before he claims the reward, Flugelman shows up with Spaghetti Nadzio, a cabaret tenor whom the detective is sure is Nino. To prove Nadzio's identity, Flugelman and Robinson arrange a radio broadcast in which the two tenors are to sing the same aria. When Rodowsky hears Nino singing, he immediately recognizes his voice but, in order to protect his brilliant "discovery," tells the police that Nino is innocent. Rodowsky then offers Nino a chance to sing at the Hollywood Bowl. Just before the performance, however, the jewel thieves send two of their henchmen to "silence" Nino, but the thugs mistake Nadzio for Nino and are later apprehended by Flugelman. Cleared of all suspicion, Nino tops off his sensational debut by singing one of Jean's compositions, which makes him a hit with both the audience and Jean.