After struggling to become a success, Betty Miller and her all-girl orchestra finally hit pay dirt when crooner Herbie Fenton comes on board. Problems arise when Betty and her girls try to find backers to invest in Herbie and they sell 125 percent of him.
Amateur band leader Betty Miller and her "sirens" perform at an orphanage benefit. Their act is followed by Herbie Fenton, a shy but talented singer, whose smooth crooning causes a New York secretary named Dorothy Dodge to faint. Although Dorothy collapsed because she was dieting too much, the audience assumes that Herbie has an overwhelming effect on women. After a photograph of Herbie and Dorothy appears in Life magazine, Betty and her band are hired for a guest radio appearance in New York on condition that Herbie perform with them. Betty makes a deal with Herbie to pay him fifty dollars a week. Dorothy, who works for a theater management company, offers Betty transportation money in exchange for twenty-five percent of Herbie's profits. In an effort to make enough money for their hotel bill, Betty inadvertently oversells stock in Herbie, which is illegal. As Herbie becomes more popular, mostly because Dorothy is paying young girls to swoon in the audience, none of the stockholders will agree to sell. Although Herbie is making considerable profits as the nation's number one crooner, Betty is unable to turn over his money until she straightens out her problem with the stockholders. Herbie's main objective is to earn $100,000 so that Betty will marry him. Betty finally decides to weaken Herbie's popularity by having him become afflicted with laryngitis before a big benefit performance. A promoter named J. J. Crawford, who has taken over Herbie's contract, however, demands that he sing. By playing a grammophone recording of Herbie singing, Betty and Herbie trick Crawford and the audience. After the performance, Dorothy points out that because Betty is only nineteen, the original contract she made with Herbie is null and void, so she cannot go to jail for overselling his stock. Betty and Herbie then sing an encore together.
