Duke brothers Randolph and Mortimer own Duke & Duke, a successful commodities brokerage in Philadelphia. Holding opposing views on the issue of nature versus nurture, they make a wager and agree to conduct an experiment, switching the lives of two people at opposite ends of the social hierarchy and observing the results. They witness an encounter between their managing director—the well-mannered and educated Louis Winthorpe III, engaged to the Dukes' grand-niece Penelope—and a poor street hustler named Billy Ray Valentine. Valentine is arrested at Winthorpe's insistence because of a suspected robbery attempt. The Dukes decide to use the two men for their experiment.