Hugo Hackenbush (Groucho Marx) is a veterinarian who masquerades as a lead doctor at Standish Sanitarium to aid the wealthy patient Emily Upjohn (Margaret Dumont). In order to save the financially failing sanitarium and its beautiful owner, Judy Standish (Maureen O'Sullivan), Hackenbush, employee Tony (Chico Marx) and jockey Stuffy (Harpo Marx) must find ingenious ways to help Gil Stewart (Allan Jones) and his inept racehorse, Hi-Hat, win the big race.