Warning: wikipedia contains spoilers
The action takes place during the French Revolution, when a secret society of English aristocrats, called the "League of the Scarlet Pimpernel", is engaged in rescuing their French counterparts from the guillotine. Their leader, the Scarlet Pimpernel, takes his nickname from the small red flower with which he signs his messages. No one except his small band of followers knows his true identity.
Marguerite Blakeney, wife of the foolish, foppish and wealthy Sir Percy Blakeney, is of French origin, and is blackmailed by the wily French revolutionary, Chauvelin, into betraying the Pimpernel - without realising that he is one and the same as her despised husband. The couple have become estranged as a result of Marguerite's denunciation of a French aristocratic family. However, all misunderstandings are eventually resolved and Percy and Marguerite return to England unscathed. Some of the subsequent books in the series deal with other characters with whom Blakeney comes into contact, and with the activities of his followers, Lord Tony Dewhurst, Sir Andrew Ffoulkes, Lord Hastings and Armand St Just.