Two musicians on the run from gangsters masquerade as members of an all-girl band.

In Chicago, in February, 1929, federal agent Mulligan sets up a raid on a speakeasy run by notorious bootlegger "Spats" Colombo, based on information provided by small-time gangster "Toothpick" Charlie. As Mulligan inspects the lively speakeasy, two members of the band, saxophonist Joe and bass player Jerry eagerly discuss plans for their salary from their first job in four months. The longtime friends begin arguing about how to spend their salary until Jerry notices Mulligan's badge and they make a hasty exit as the raid begins, avoiding the police roundup. Putting up their coats as collateral, they place a bet with their bookie, and promptly lose both the bet and their coats. Desperate, Joe and Jerry visit the musicians' agency building hoping to line up another job. At Sid Poliakoff's agency, receptionist Nellie Weinmeier, incensed over being stood up by Joe a few nights earlier, reveals there is an opening for a bass and sax with a band in an all-expenses paid trip to Florida. Joe and Jerry eagerly question Sid, only to learn that the positions are in an all-girl band. Sid tells them of a job at a college dance in Urbana and Joe accepts, then charms Nellie into loaning them her car for the Urbana gig. Retrieving the car at a garage owned by Toothpick Charlie, Joe and Jerry unintentionally witness Spats and his men shoot Charlie and his men to death for informing on the speakeasy. Although the musicians are spotted by Spats, he is distracted by Charlie, who revives long enough to allow Joe and Jerry to flee. After they evade the gangsters, Jerry suggests they call the police, but Joe reminds him they will not be safe from Spats in any part of Chicago in spite of the police. Joe then telephones Sid and, using a high falsetto voice, accepts the job with the all-girl band. That evening at the train station, Joe and Jerry, uncomfortably disguised as women, check in with band leader Sweet Sue and manager Beinstock as the newest members of the Society Syncopators, Joe as Josephine and Jerry as Daphne. Once on board the train, Joe fears that Jerry's enthusiasm at finding himself among so many women will expose them and warns his friend to behave "like a girl," but in the process, musses Jerry's outfit. Retreating to the ladies' room for repairs, the men come upon stunning singer and ukulele player Sugar Kane Kowalczyk drinking bourbon from a flask. Sugar pleads with them not to report her to Sue, who has threatened to fire her if she is caught drinking again. A little later during rehearsal, when Sugar's flask falls to the floor, Sue responds angrily, but Jerry steps forward, and to Sugar's surprise, claims the flask is his own. That night, Sugar sneaks to Jerry's berth to thank him for his action, then abruptly jumps into the berth to avoid Sue. Overwhelmed by Sugar's proximity, Jerry grows anxious and suggests that he needs a drink and within minutes an impromptu party ensues at Jerry's berth. Joe awakens and is horrified, but gets drawn into the festivities when Sugar asks him to help break up an ice block in the ladies' room. There Sugar confides that she is with the all-girl band in order to escape a series of unhappy love affairs with tenor saxophone players and dreams of finding a sensitive millionaire who wears glasses. Upon arriving in Florida at the beachfront Ritz Seminole Hotel, "Daphne" catches the attention of wealthy, oft-married Osgood Fielding III. Once in their room, Jerry, infuriated at being flirted with and pinched by Osgood, demands they give up their disguises and find a male band, but Joe insists they must maintain their masquerade, as Spats will surely investigate male orchestras all over the country. Jerry reluctantly agrees and then accompanies Sugar to the beach. Unknown to Jerry, Joe has stolen Beinstock's suitcase of clothes and eyeglasses and, dressing in them, goes to the beach where he stages an accidental meeting with Sugar. Joe implies that he is the heir to the Shell Oil company and, captivated by the apparently sensitive "Junior," Sugar invites him to the band's opening that night. Back in their room, Jerry receives a call from Osgood inviting Daphne to a candlelit dinner on board his yacht. Joe accepts for Jerry, then tells his protesting friend that he must keep the date with Osgood on shore, as he, in the guise of Shell Oil, Junior, plans to dine with Sugar on Osgood's yacht. That night during the band's performance, Osgood sends Jerry an enormous bouquet, which Joe commandeers to give to Sugar with a card inviting her to dine with Junior. Afterward, Joe meets Sugar on the pier as an unhappy Jerry talks Osgood into dining at a local roadhouse. While Jerry and Osgood tango to the music of a Cuban band at the roadhouse, on board Osgood's yacht Joe convinces Sugar that a romantic emotional shock in his youth has left him impotent and years of expensive medical treatment have failed to cure him. Appalled, Sugar begs Joe to allow her to help, but after numerous passionate kisses, Joe insists he is unmoved. Determined, Sugar pleads to keep trying and Joe agrees. At dawn, Joe climbs back in the window of the hotel room to find Jerry deliriously happy because Osgood has proposed. Taken aback, Joe tells his friend it is impossible for him to marry another man, but Jerry explains his plan to reveal his identity after the marriage ceremony and, after an annulment, force Osgood to pay him alimony. Disturbed by Jerry's high spirits, Joe urges him to remember that he is a boy, and Jerry sadly wonders what to do with Osgood's engagement gift, an extravagant diamond bracelet. The next day, gangsters from all over the country, summoned by mob boss Little Bonaparte, meet at the hotel under the guise of attending an opera convention. Mulligan is also present and when Spats arrives, accuses him of the murder of Toothpick Charlie and his gang. Upon spotting Spats in the lobby, Joe and Jerry panic and realize they must flee. In their room, Jerry laments having to give up Osgood and Joe telephones Sugar to disclose that Junior's family has ordered him to Venezuela immediately for an arranged marriage. Moved by Sugar's despair, Joe places the diamond bracelet in a box of flowers and pushes it across the hall to her door as a farewell gift from Junior. Joe and Jerry then escape out of their hotel window but are seen by Spats and his men on the floor below. When the pair dash away leaving their instruments behind, Spats finds bullet holes in Jerry's bass and realizes the "broads" are the Chicago murder witnesses in disguise. Knowing they have been discovered, Joe and Jerry dress as a bellboy and a wheelchair-bound millionaire and head across the lobby filled with Spats's men. Noticing that Jerry has inadvertently left on his high heels, the henchmen give chase and Joe and Jerry run into a convention hall and hide, unaware that the mob "convention" is scheduled to meet there. Moments later, Spats sits at the table under which Joe and Jerry are hiding, and in a prearranged plan, Bonaparte pretends to honor Spats by presenting him with a giant cake, out of which bursts an assassin who guns down Spats and his men. Terrified, Joe and Jerry bolt, but as Bonaparte orders them found, Mulligan and his men close in to make arrests. Resuming their disguises as women, Joe and Jerry overhear that the remainder of Bonaparte's men are watching all buses and trains out of town and Joe decides they should escape on Osgood's yacht after Jerry elopes with him. When Jerry balks, Joe says their only option is certain death by Bonaparte's men. While Jerry telephones Osgood to make arrangements, Joe hears Sugar and the band finishing a song and climbs onto the stage to tell her that no man is worth her heartbreak, then kisses her before hurrying away. Realizing that "Josephine" is "Junior," Sugar follows the men down to the dock and the waiting Osgood. As they all board the speedboat, Joe removes his wig and confesses that he is a liar and a phony, but Sugar insists that she does not care and the couple embrace. Meanwhile, Osgood proudly tells Daphne that his mother is delighted about their upcoming wedding. Jerry nervously confesses that he cannot marry him, declaring that he is not a natural blonde, smokes, has lived in sin and cannot bear children, but Osgood remains cheerfully undaunted. At last Jerry snatches off his wig and admits that he is a man, wherein Osgood happily assures him that, after all, "nobody's perfect."