The events of the French Revolution cause tremors of unease in English aristocratic society. Reports of a mysterious Englishman, known as the Scarlet Pimpernel, who engineers daring rescues of condemned aristocrats and escorts them safely to England, have resulted in much speculation as to his true identity.

In France, the Count and Countess de Tournay and their daughter Suzanne are about to be taken to their execution when the Count is told that Robespierre wishes to speak with him and he is taken from his family. A decoy appears on the rooftops shouting anti-republican slogans; in the resultant chaos, the de Tournays are smuggled into a covered wagon driven by a decrepit old woman. She safely drives them through the checkpoint and to safety: the 'old woman' is in fact the Scarlet Pimpernel.

The Pimpernel, in reality an English aristocrat named Sir Percy Blakeney, learns from his men that de Tournay was for some reason removed before his execution, and that the new Ambassador to England, Citizen Chauvelin, has left London and returned to Paris. Blakeney describes Chauvelin as their biggest enemy.

Robespierre officially entrusts Chauvelin with the task of finding the Pimpernel. Chauvelin points out that, since he presumably speaks perfect French, the Pimpernel is surely an aristocrat himself, and that it is only a matter of time before he tracks him down via his contacts in London society. De Tournay is brought in and offered his life on condition that he assists in the job of detection, but he refuses and is sent back to prison.

Madame de Tournay and her daughter arrive safely in England in the care of the Pimpernel's confederates. Blakeney tells his men that in order to maintain their secret they must endure the humiliation of pretending to be superficial and cowardly fops. When another nobleman enters the room he immediately assumes just this persona, and irritates the man with a display of foolish behaviour and posturing.

Chauvelin's agents intercept a note sent by Armand St Just, Marguerite's brother and another of the Pimpernel's allies, to his second-in-command Sir Andrew Ffoulkes, warning him of Chauvelin's interest. Chauvelin decides to watch Ffoulkes, and to secure Marguerite's cooperation by having her brother arrested. On hearing of this, she tearfully consents to his wish that she should become a spy in English society and attempt to identify the Pimpernel, unaware that it is her husband.

At a party, Marguerite feigns dizziness while dancing with Ffoulkes and has him take her out of the room so that she can discover the contents of a note he was handed earlier in the evening. She learns that he has arranged to meet the Pimpernel in the library at midnight and informs Chauvelin, who enters the library to keep watch, only to find Sir Percy asleep. He also falls asleep and finds a mocking note from the Pimpernel on his lap when he wakes.

Marguerite explains her quandary to Percy, who is planning another trip to France to free de Tournay and Armand. He decides for her sake to retain his secret until he has safely returned. After he leaves, however, she notices a pimpernel motif on the ring of one of his ancestors in an old portrait and realises the truth. A letter from Chauvelin reveals that he too has finally discovered the Pimpernel's identity. She goes to Ffoulkes for help, and they decide to travel to France to warn Percy that he is walking into Chauvelin's trap.

Posing as soldiers, the Pimpernel and his confederates free Armand and de Tournay, but Chauvelin is waiting for them - with Marguerite now captive - at the rendezvous point for their return to England. In return for having Marguerite put safely on his ship, Sir Percy agrees to stand before Chauvelin's waiting firing squad. He is led outside and shots are heard. But it is another deception: Chauvelin's men have been overpowered and replaced by the Pimpernel's. Chauvelin is locked in the cellar and Sir Percy and his associates make good their escape. On the ship, Sir Percy and Marguerite see the advancing shores of England.