A riverboat gambler has to choose between his true love and the woman who''''s his lucky charm.

Frankie and Johnny, singers on Clint Braden's riverboat, are in love, but Frankie refuses to marry Johnny until he stops gambling and losing all his earnings. A gypsy fortune-teller predicts that a redheaded woman will appear and can reverse Johnny's fortune. Soon after, redheaded Nellie Bly, Clint's former girl friend, comes aboard the riverboat, and Johnny begins to win. Meanwhile, Cully, Johnny's piano-playing sidekick, writes a song, "Frankie and Johnny," that is introduced on the showboat. A music publisher hears the song, likes it, and invites Frankie and Johnny to come to New York City to perform. Hopeful that Nellie's presence will bring him luck, Johnny tries to win enough money to take him and Frankie to New York. Frankie becomes jealous of Nellie, who is only interested in marrying Clint, and breaks off with Johnny; at the same time, Clint admonishes Johnny, telling him to stay away from Nellie. At the Mardi Gras ball in New Orleans, Nellie and Frankie dress exactly alike, and Johnny, thinking he is with Nellie, gambles and wins. When Frankie unmasks, Johnny realizes that she brings him as much luck as Nellie. Clint's dim-witted bodyguard, thinking that he is looking out for his employer's interests, places real bullets in the gun Frankie uses to "shoot" Johnny in the musical number. Luckily, the bullet lodges in a charm Frankie had given Johnny, and he is unharmed. Frankie and Johnny decide to marry, as do Nellie and Clint.