"Big" Jim Stevens, undisputed boss of the Chicago underworld, gets an unexpected birthday present from his ambitious lieutenant, Guy Gisborne. Instead of a stripper popping out of the cake, Big Jim gets shot by all the guests. Gisborne takes over. He orders all the other gangsters in town to pay him protection money. The news does not sit well with Big Jim's friend and fellow gangster, Robbo, and a gangland war breaks out.Robbo (Frank Sinatra) recruits pool hustler Little John, who demonstrates his pool skills while singing, plus quick-draw artist Will and a few other hoods, but they are still greatly outnumbered. In addition, the corrupt Sheriff Octavius Glick is on Gisborne's payroll. Gisborne and Robbo come up with the same idea, to destroy the other's gambling joint on the same night.Big Jim's refined, well-educated daughter, Marian, shows up. She asks Robbo to avenge her father's death (wrongfully attributed to the sheriff), a request which Robbo flatly refuses. Gisborne disposes of the sheriff. Marian then invites Robbo to dinner and gives him $50,000, thinking that Robbo did as she had asked. Robbo refuses the money, but Marian attempts to seduce him into joining forces to take over the whole town. Robbo turns her down. When she sends the money to his under-repair gambling club, Robbo donates it to a boys' orphanage. Alan A. Dale, the orphanage's director, notifies the newspapers about this good deed. A new Chicago star is born: a gangster who robs from the rich and gives to the poor.Robbo finds it useful to have the public on his side. He invites the delighted Dale to join his gang, having him handle all the charities. Dale starts the Robbo Foundation and opens a string of soup kitchens, free clinics and orphan shelters. He even gives green, feathered hats and bows and arrows to the orphans, while thoroughly milking the Robin Hood image. In the meantime, Robbo and Little John teach Dale a little about "Style."Robbo's joint re-opens and it is a hit. Gisborne, whose place is now empty, is infuriated. He and the new sheriff, Potts, organize a police raid. Robbo has anticipated this; when a few switches are pulled, the entire club is disguised as a mission. The sheriff and Gisborne burst in to find Robbo's gang singing gospel songs and preaching the sins of alcohol, complete with hymnals and tambourines ("Mr. Booze").Robbo is framed for Glick's murder. At the trial, Gisborne and Potts claim that Robbo planned the whole thing. Dale tries to teach the despondent orphans to view this as a lesson ("Don't Be a Do-Badder"). The jury finds Robbo innocent. He thanks them ("My Kind of Town"). When he returns to his club, Robbo finds every one of his charities is now a front for counterfeiting. The soup kitchen smuggles fake bills in soup cans over state lines. Robbo also finds Little John living it up in Marian's mansion. Marian is willing to keep Robbo as a front, as long as she is in charge. Robbo shows his contempt for her and leaves. Little John decides to go with him.Marian finds another willing partner in Gisborne. However, the gangster is not a match for Robbo and ends up dead. Robbo tells a shocked Marian to clear out of town. She instead turns public opinion against him, starting a Women's League for Better Government and framing Robbo for the counterfeiting ring that she and Little John started. Unable to fight an angry mob of women, Robbo and his gang flee.Robbo and his merry men are reduced to working as Santa Clauses to solicit charitable donations. They watch dumbfounded as Marian steps out of a car with her latest partner, Alan A. Dale. He casually gives them money before going off with Marian.