In turn-of-the-century New York City, con artist Peaches O'Day befriends Captain Jim McCarey, a cop who must turn her in unless she leaves town. The clever Peaches returns transformed as sultry brunette and Parisian sensation Mademoiselle Fifi. After catching her show, a crooked mayoral candidate tries to shut it down when Peaches demurely declines his romantic overtures. McCarey jumps in the race for mayor, and the loyal Peaches fervently campaigns for him.