In Mexico, dancer/singer Lita Valdez is fired from the cantina where she performs after she refuses to entertain a male customer at his table. When her younger brother Alberto, whom Lita calls "Baby," arrives to tell her that he has quit college in the United States to become a professional fighter, Lita insists that he knock down her boss. Instead, Baby accidentally knocks out a customer, who happens to be a boxer. Fight promoter Doc Hogan is impressed with Baby's punch, and offers to represent him in New York City. There Lita is managing her brother's affairs while he is training when Hogan's other fighter, Jerry O'Leary, runs into her and the two are immediately attracted to each other. Baby then wins his first fight, and Lita watches all the fights to see the two men in her life, Baby and Jerry. One night at Perrone's nightclub, Baby meets Flossie Rankin, a singer, and falls in love. Jerry's manager, Al Johnson, arranges for Lita to sing with Flossie's band as a joke, but when she is a surprise hit with the audience, Perrone hires her and headlines her with Flossie. Baby, meanwhile, fights his way to the top of his rank, and despite Lita's protests, the boxing commission insists on matching Baby and Jerry in a fight. Al, hoping to make a bundle on a bet, spreads gossip that Baby is going to be the favorite, but plots with Flossie to interfere with Baby's training so that he loses the fight. One night after Baby comes home drunk, Lita confronts Flossie at her apartment. The women get into a furious fight, and Lita forces Flossie to admit her scheme to Baby. Baby absolves Flossie but rejects Lita because of her continual interference. Lita then refuses to see Jerry because she believes he was in on the set-up. Although Flossie seems to be playing along with Al, she has genuinely fallen in love with Baby and helps him train because he hopes that Jerry will return to studying medicine if he loses. Although the fight is difficult, Baby wins and Al loses his bet. Estranged from both men in her life, Lita continues performing at Perrone's. After several months, Flossie comes to see her at the nightclub and assures Lita that Jerry was never involved in the set-up. A delighted Lita then reunites with both Jerry and Baby, who have enlisted in the U.S. Army and Mexican Army, respectively, and are waiting for her in the club.