Sweeney Bliss, champion mule raiser in Missouri, takes his prize mule Samson to London, where the British government is trying to decide whether to buy mules or tractors for its colonial troops. He is accompanied by his ritzy wife Julie who has high society aspirations and hopes to have her younger sister Lola Pike marry a British diplomat. Complicating matters is a business rival, Porgie Rowe, who is trying to sell tractors to the government and keeps knocking Sweeney's prize Missouri mules.