The scene is set in the terrorized Paris of revolutionary France in the 1800's. During this time period nobody was safe from the horrifying grasp of,,Madame la Guillotine" which claimed hundreds of lives every day.
The Scarlet Pimpernel is England's national hero, a rescuer of French aristocrats from under the guillotine in France. He's also Sir Percy Blakeny, husband of Marguerite Blakeney nee St. Marguerite's brother Armand is under suspicion in France and a French government agent, Chauvelin, approaches her with an ultimatum: discover the identity of the Pimpernel or let your brother die.
When she realizes that the Pimpernel is her husband, she's off to warn and rescue him with the help of another member of the League of the Scarlet Pimpernel, Sir Andrew Ffoulkes. Chauvelin threatens to kill Marguerite's brother if she warns her husband that Chauvelin is trying to kill him.