A policeman, fireman, and boxing manager live with their mother; the boxer wins over his brother's girlfriend in this family comedy.
Policeman Pat O'Hara (Pat O'Brien) tells Danny O'Hara (James Cagney) to get a job, because he wants to get married; but Danny won't take the police exam. He asks Ma (Mary Gordon) to invest $15 in his new boxer, Carbarn Hammerschlog (Allen Jenkins), who whenever he hears a bell, starts boxing. Pat invites Captain Jackson's daughter Lucille (Olivia de Havilland) for dinner and calls Ma. Danny jogs with Carbarn and tells him no dames. Danny and Carbarn pull Lucille from under a car. Danny changes the tires while Carbarn smokes. Danny tells him not to smoke. Ma instructs fireman son Mike O'Hara (Frank McHugh) in manners. Pat has no suit, because Danny gave it to Carbarn. Lucille comes in, and Ma mistakenly mentions Pat's marriage hopes. Danny comes in and smiles at Lucille. A bell causes Carbarn to punch Mike and Pat, who is attended by a doctor. Danny takes Lucille in her car, and they stop for a steak.
At the Fireman's Ball the three sons dance with their mother and with Lucille. Danny tells her he's falling for her and kisses her. Pat interrupts and later slaps Danny. Pat packs to leave and gets angry at Danny. Ma slaps Pat, and Danny says he should go instead. Danny kisses Ma and leaves. Pat kisses Ma goodnight. Jackson and Pat plan a fight between the champ Delancey and Carbarn. Danny trains a reluctant Carbarn and boxes with him. A man asks Danny to have Pat forget a ticket and gets slugged by Danny. Lucille asks Danny why he left home and says he and Pat are being silly, because she's not in love with Danny either. Lucille tells Ma she is upset and admits she loves Danny. Ma gives Danny soup and hopes he'll marry Lucille.
Carbarn hears that Delancey killed a man in the ring. Mike gives him gin for a toothache, but Carbarn keeps swallowing it; they both get drunk. In the locker-room Carbarn hears a bell and starts fighting; Delancey knocks him out. Pat goes to get Carbarn, and Danny decides to box in his place. Danny is knocked down several times; but after his brothers Mike and Pat help him, he starts winning. Lucille tells Pat to tell Danny she loves Danny, and Danny wins.
The comedy and sentiment among the family are pleasantly entertaining; but the boxing plot is far-fetched and brutal. The sons' devotion to their mother is heart-warming, and their conflicts with each other are understandable.