In February 1929, in Prohibition-era Chicago, Joe is a jazz saxophone player and an irresponsible, impulsive ladies' man; his anxious friend Jerry is a jazz double bass player. They work in a speakeasy owned by gangster "Spats" Colombo. Tipped off by informant "Toothpick" Charlie, the police raid the joint. Joe and Jerry escape, but later accidentally witness Spats and his henchmen gunning down "Toothpick" and his gang in revenge, which was inspired by the real-life Saint Valentine's Day Massacre.[6] Spats and his gang see them as they flee. Broke, terrified, and desperate to get out of town, Joe and Jerry disguise themselves as women named Josephine and Daphne so they can join Sweet Sue and her Society Syncopators, an all-female band headed by train to Miami. On the train, Joe and Jerry befriend Sugar Kane, the band's vocalist and ukulele player.
Joe and Jerry become obsessed with Sugar and compete for her affection while maintaining their disguises. Sugar confides to "Josephine" that she has sworn off male saxophone players, who have taken advantage of her in the past. She hopes to find a gentle, bespectacled millionaire in Florida. During the forbidden drinking and partying on the train, "Josephine" and "Daphne" become close friends with Sugar, and struggle to remember that they are supposed to be girls and cannot make passes at her.
The film's trailerOnce in Miami, Joe woos Sugar by assuming a second disguise as millionaire Junior, the heir to Shell Oil while feigning indifference to her. An actual millionaire, the much-married, aging, mama's-boy Osgood Fielding III, persistently pursues "Daphne", whose refusals only increase his appetite. He invites "her" for a champagne supper on his yacht, New Caledonia. Joe convinces Jerry to keep Osgood occupied onshore so that "Junior" can take Sugar to Osgood's yacht and pass it off as his own. Once on the yacht, "Junior" tells Sugar that psychological trauma has left him impotent and frigid, but that he would marry anyone who could cure him. Sugar tries to arouse him, with considerable success. Meanwhile, "Daphne" and Osgood dance the tango ("La Cumparsita") till dawn. When Joe and Jerry get back to the hotel, Jerry announces that Osgood has proposed marriage to "Daphne" and that he, as Daphne, has accepted, anticipating an instant divorce and huge cash settlement when his ruse is revealed. Joe convinces Jerry that he cannot marry Osgood.
The hotel hosts a conference for "Friends of Italian Opera", which is a major meeting of the national crime syndicate, presided over by "Little Bonaparte". Spats and his gang recognize Joe and Jerry as the witnesses they have been looking for. Joe and Jerry, fearing for their lives, realize they must quit the band and leave the hotel. Joe conceals his deception from Sugar by telling her, over the telephone, that he, Junior, must marry a woman of his father's choosing and move to Venezuela for financial reasons. Sugar is distressed and heartbroken. Joe and Jerry evade Spats' men by hiding under a table at the syndicate banquet. "Little Bonaparte" has Spats and his men killed at the banquet; again, Joe and Jerry are witnesses and they flee through the hotel. Joe, dressed as Josephine, sees Sugar onstage singing a lament to lost love. He runs onto the platform and kisses her, causing Sugar to realize that Josephine and Junior are the same person.
Jerry persuades Osgood to take "Daphne" and "Josephine" away on his yacht. Sugar runs from the stage at the end of her performance and jumps aboard Osgood's launch just as it is leaving the dock with Joe, Jerry, and Osgood. Joe confesses the truth to Sugar and tells her that she deserves better, but Sugar wants him anyway, realizing he is the first man to genuinely care for her. Meanwhile, Jerry tries to get out of his promise to marry Osgood, by listing reasons why "Daphne" and Osgood cannot marry, ranging from a smoking habit to infertility. Osgood, smiling broadly, has answers for all of them. Exasperated, Jerry rips off the wig, switches to his normal voice, and says "I'm a man!" Still smiling, Osgood replies "Well, nobody's perfect", leaving Jerry speechless.
