Navy seaman Benny Linn (Groucho Marx) is flabbergasted when his pal, Navy seaman Tim Dunnovan (William Bendix), squanders his inheritance on Little Erin, a horse he's never seen. Talking their put-upon superior into granting them five days' leave in order to unswindle Dunnovan, Benny sets to shore with purpose and chicanery in mind. Tracking down the horse's trainer (Gene Lockhart), the salts discover their seemingly lame horse has a secret twin -- Little Shamrock -- owned by lovely carhop Jane Sweet (Marie Wilson). Fake Southern gentlemen, switched and double-switched equines, angry gangsters, stumbling saboteurs and one henpecked businessman (Don DeFore), who may just be Jane's true love - in order to save the day, it's time for Groucho to ride.