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.
When the tiny nation of Freedonia goes bankrupt, its wealthy benefactor, Mrs. Teasdale (Margaret Dumont), insists that the wacky Rufus T. Firefly (Groucho Marx) become the country's president. Sensing a weakness in leadership, the bordering nation of Sylvania sends in the spies Pinky (Harpo Marx) and Chicolini (Chico Marx) to set the stage for a revolution. As Firefly clashes with the Sylvanian ambassador (Louis Calhern), plenty of mayhem ensues, and the countries verge on all-out war.
The Marx Brothers run amuck in the world of opera when Otis B. Driftwood (Groucho Marx) meets aspiring singer Ricardo (Allan Jones), who is determined to win the love of fellow performer Rosa (Kitty Carlisle). Aided by Fiorello (Chico Marx) and Tomasso (Harpo Marx), Otis attempts to unite the young couple, but faces opposition from the preening star Lassparri (Walter Woolf King), who also has his sights on Rosa. Traveling from Italy to New York, Otis and friends rally to try and win the day.
