Revolutionary France. The Terror is in full swing. Hundreds of people are being sent to the guillotine, but some aristocrats are lucky enough to be saved by a mysterious Englishman, known only as the Scarlet Pimpernel.

Revolutionary official Chauvelin is signing death warrants when St Juste, a member of the increasingly powerless National Assembly, comes to request a permit to visit England. He wants to visit his sister Marguerite, who has married Sir Percy Blakeney, an English nobleman. Chauvelin, however, does not want St Juste to go. As Chauvelin finishes a drink, he sees writing at the bottom of the glass. It is a message from the Pimpernel telling Chauvelin he is in London.

At Boodles Russian Bath in London, a group of young men enjoy the steam room. When a group of older statesmen enter, Sir Percy Blakeney, one of the younger men, begins teasing them, and recites a poem he has composed about the exploits of the elusive Scarlet Pimpernel. They are interrupted by the arrival of the Prince of Wales, who seeks the foppish Sir Percy's advice on his newly tailored jacket. Sir Percy relishes his role as a frivolous dilettante as it provides cover for his true identity as the Scarlet Pimpernel.

In France, the Pimpernel and his men rescue the aristocratic Tournai family from an angry mob and escort them to the refuge of Mont St Michel and then on to England. Once across the channel, the émigrés stop at an inn. Lady Marguerite Blakeney arrives and is greeted coolly by her husband and with hostility by the Countess Tournai. Percy's friend Sir Anthony asks him what has gone wrong with his marriage; Percy tells him that he found out that Marguerite was responsible for denouncing a family who were then sent to the guillotine. Although Percy despises what she did, he admits he is still in love with her.

Chauvelin arrives in England as the new French Ambassador, and is determined to discern the identity of the elusive Pimpernel. At Lady Grenville's ball, he blackmails Marguerite, telling her he has intercepted an incriminating letter from her brother St Juste to Sir Percy. Chauvelin threatens to have St Juste executed unless Margeurite helps him to unmask the Pimpernel. She tells Percy her plight and he promises to help her, telling her he will use his influence with the Prince. He dons a disguise and attempts to retrieve the letter from the French Embassy, but is discovered by Chauvelin. Although Sir Percy escapes, Chauvelin's suspicions are aroused, as only he, his men, and Marguerite know about the existence and location of St Juste's letter. Meanwhile, Sir Percy sends a message to Sir Andrew, who is another of his followers. Marguerite, now determined to discover who the Pimpernel really is, finds this letter and when Chauvelin threatens her brother's life again, she reluctantly tells him that the Pimpernel is on his way to France. She confesses what she has done to her husband, who then asks her about her previous betrayal. Marguerite tells him that she made the mistake of believing Chauvelin was her friend, and that it was actually he who denounced the family. With his love reawakened, Percy sets off for France. Back at their home, Marguerite discovers the Pimpernel's secret seal and realises that her husband is the elusive hero. Horrified at her betrayal, she enlists the help of Sir Anthony to rescue Percy from Chauvelin's clutches; together they race to France.

Marguerite and Sir Anthony go to Mont St Michel but, unbeknown to them, Chauvelin has had them followed. He is waiting when the Pimpernel and his men arrive. Sir Percy surrenders to save Marguerite and relinquishes his pistol to Chauvelin. He is taken to face the firing squad and Chauvelin listens to the gunfire, relieved to finally be rid of his enemy. He is shocked when Percy returns, having previously substituted Chauvelin's firing squad with his own men. The desperate Chauvelin tries to shoot Percy, but Percy jauntily tells him that the Pimpernel's men never use loaded guns. The league and yet more rescued aristocrats return to England with Percy and Marguerite, who are now happily in love.