Based on the comic strip by Ham Fisher, the son of a boxer gets a manager who lines up fixed championship fights, as the champ enjoys a new girlfriend.
Pete Palooka (Robert Armstrong) promises his wife Mayme (Marjorie Rambeau) he'll come back after his championship fight; but she finds him with blonde Trixie (Thelma Todd) and with her son leaves him.
Twenty years later Joe Palooka (Stuart Erwin) is discovered in the country by manager Knobby Walsh (Jimmy Durante). Joe tells his girlfriend Anne (Mary Carlisle) he's going to be a boxer, and he gets his mother's permission to leave. Knocked out in his first round, Joe nonetheless is given a championship fight against Al McSwatt (William Cagney). Mayme hears of the fight and sends a telegram hoping he gets knocked out. McSwatt comes in drunk with Nina Madero (Lupe Velez). Joe hits him in the stomach and wins. Nina congratulates Joe and invites him to the Paradise Club, where she sings and dances. Knobby rips up Joe's telegram from Anne as "another dame." Nina gives Joe a drink in her apartment and spills it on his pants so he'll have to take them off. Knobby brings Joe a cable from his dad and gets him to leave to see his ma. Knobby woos Nina, and she slaps him. McSwatt arrives, but Nina has him thrown out.
Nina goes out with Joe, and they pose kissing for an ad. Knobby hires mugs to lay down for Joe, who wins several fights that way. Joe has a diamond bracelet for Nina, but Knobby says she loves the championship. Mayme arrives and asks Knobby where Joe is. Joe drinks with Nina at the nightclub. Knobby tells Joe his ma is in town, but he doesn't believe him. They drink to their mothers, and Knobby is thrown out. McSwatt takes Nina's coat, and Joe wants to fight, agreeing to a match. Drunk Knobby sings "Inky Dinky Doo." Mayme tells Joe that she put him to bed, and she asks about Anne. Joe says he has changed as champion. Nina comes in, and Mayme asks her to give up Joe. Nina says she loves Joe. Knobby tells Joe the fights were set-ups.
Pete Palooka arrives, sees Mayme, meets his son Joe, and offers to train him. Mayme doesn't want Joe to fight. Knobby tells Blacky (Stanley Fields) to bet on Joe, but he has trainer Whitey (Tom Dugan) bet against Joe. Anne and Mayme watch Nina kiss Joe good luck. Joe knocks McSwatt down; but as Joe is getting beat up, Mayme and Anne leave. Nina urges McSwatt to finish off Joe, and Pete throws in the towel. Afterward Pete hits McSwatt and gets a black eye. Mayme tells Joe she is happy. Joe makes up with Anne and gets a message from Knobby that he bet their money on McSwatt. In the final scene Knobby has married Nina, and they have a baby that looks like Knobby.
Durante adds comic flair to this story about fixed boxing. The innocent young man is tempted away from his country sweetheart by a fast city woman.