The Flying Inn is set in a future England where the Temperance movement has allowed a bizarre form of "Progressive" Islam to dominate the political and social life of the country. Because of this, alcohol sales to the poor are effectively prohibited, while the rich can get alcoholic drinks "under a medical certificate". The story relates the adventures of Humphrey Pumph and Captain Patrick Dalroy, who roam the country in their cart with a barrel of rum in an attempt to evade Prohibition, exploiting loopholes in the law to temporarily prevent the police taking action against them. Eventually the heroes and their followers foil an attempted coup by an Islamic military force.