Johnny and girlfriend Frankie are performers on a Mississippi River riverboat, which also has a casino. Johnny is a compulsive gambler who is down on his luck and in debt.
Johnny and his friend Cully, a musician and composer, visit a gypsy camp to get his fortune told. A lady reads tea leaves and tells Johnny that he will soon meet a red-haired woman who will bring him luck.
Back on the boat, Johnny and Cully promptly encounter Nellie Bly, their boss Clint Braden's on-again, off-again girlfriend. Nellie has just caught Braden seducing another singer, Mitzi. Since she has red hair, Nellie is persuaded by Johnny to touch his chips for luck. After he wins, Johnny is convinced that the gypsy must be correct.
Frankie finds out and becomes jealous, as does Johnny's boss. In a bit of musical theatre, Frankie shoots Johnny for dancing with Nellie Bly while singing Cully's new song. A Broadway recruiter sees the riverboat show and buys the rights to this new song, suggesting that Frankie and Johnny should work together with him in New York.
Landing in New Orleans, the musical cast and riverboat crew attend a masked ball. Frankie, Nellie and Mitzi each rent the same Madame Pompadour costume.
Johnny is eager for the luck of redhead Nellie to win more money, contrary to Frankie's expressed wishes. Being masked and in costume, Frankie and Nellie scheme to switch places to test Johnny's lucky-redhead theory. Johnny wins ten thousand dollars at a roulette wheel, but when he kisses the woman he believes to be Nellie, he discovers the switch. Frankie is furious. She throws the winnings out the window.
Blackie, a dim-witted stooge who works for the boss, hears Braden drunkenly complain about how he has lost Nellie. Thinking he can be of help, Blackie switches the blank cartridge in Frankie's stage gun for a real bullet.
The boss tries to prevent the impending disaster, but arrives at the theatre too late. Frankie has shot Johnny for real. Frankie forgives his gambling as the love of her life appears to be dying on stage. Johnny then stands up, apparently unhurt. Johnny was saved because the bullet struck a lucky medallion he was wearing that Frankie had given him.