The Portorican prime minister asks British detective Sherlock Holmes to find a twin for King Fernando XXIII, a weak and frightened man who fears anarchists and does not want to show himself in public. Holmes finds in the Czech newspapers a photo of the perfect double, František Lelíček, a daring bon vivant drowned in debt, so when Holmes offers him money, Lelíček decides to travel to Portorico and play the role.