While Mame Walsh is away on vacation, her younger sister, Janie, begins a flirtation with Mame's sweetheart, Bill Billingsley, who clerks in the same department store where they work. Mame stages a surprise party for Bill, at which she plans to accept his proposal, until she sees Janie secretly kissing him and announces she will adopt Janie's philosophy of "love 'em and leave 'em." She begins an obvious flirtation with Lem Woodruff, a petty crook and gambler. Janie, meanwhile, having dissipated the funds of the department store's welfare club in racetrack betting, tries to recover her losses with Lem's help. Miss Streeter, the club president, threatens to prosecute, and Janie places the blame on Mame. The store masquerade finds Janie dancing with doubt-torn Bill and flirting with manager McGonigle, thereby winning promotions for all; and Mame, retrieving the club funds from Lem, is reunited with Bill.