When wounded robber Rocks Dawson demands to be treated by pharmacist Joe McCabe, Joe arrests the robber and becomes a hero. Joe is the younger brother of nightclub singer Tommy McCabe, whose act includes a parody of a police officer. Tommy's cavalier attitude toward the police department raises the ire of audience member Jerry Sullivan, who invites Tommy to her house for dinner. When Tommy calls on Jerry, he is embarrassed to learn that her father and cousins are all police officers, but wins the family over with his rendition of "When Irish Eyes Are Smiling." Falling in love with Jerry, Tommy foresakes performing to join the police academy, where he is assigned to instructor Sergeant Bill Morrissey, his rival for Jerry's affections. Tommy's insubordination irritates Bill, and consequently, after graduation, Tommy is assigned to the police glee club. When Bill opposes Tommy's request for a transfer, Tommy socks Bill and is suspended from the force. Meanwhile, Jerry has fallen in love with Tommy, who visits Joe at the pharmacy to tell him the good news. While the brothers are talking, members of Rock Dawson's gang break in and kill Joe to avenge Rock's arrest. The gang has been conducting a murderous rampage, and the police are hot on their trail. Out of compassion, Jerry's father allows Tommy to accompany him to the factory district where his brother's killers are trapped. As Bill enters the compound, he is taken hostage by the gang. Tommy convinces Lieutenant Sullivan to give him five minutes to capture the killers, and climbs into the building, saves Bill and brings the killers to justice. For his bravery, Tommy is reinstated in the police force, thus rewarding Jerry's faith in him.