The novel is set during the Reign of Terror following the start of the French Revolution. Sir Percy is a wealthy English baronet who rescues individuals sentenced to death by the guillotine. He soon reveals himself to be a master of disguise, an imaginative planner, a formidable swordsman and a quick-thinking escape artist. With each rescue he taunts his enemies by leaving behind a card showing a small flower—a scarlet pimpernel. The identity of the Scarlet Pimpernel thus becomes a topic of widespread popular interest and the hero himself becomes the subject of an international manhunt by the French revolutionary authorities. To hide his true identity, Sir Percy presents himself in everyday life as a dim-witted, foppish playboy. His secret is kept by a band of friends known as the League of the Scarlet Pimpernel. The league operates as an undercover team in enacting Sir Percy's rescue plans.
