Theme
I would say that the main theme of the Scarlet Pimpernel is Loyalty. Loyalty to one's country, one's family, one's husband/wife etc. Marguerite must choose between her loyalty to her country, France, and her loyalty to her husband. She is also torn between her loyalty to the Scarlet Pimpernel whose actions she strongly believes in, and her loyalty to her brother Armand. In the end she chooses passion over what is proper (serving her country through Chauvelin). She loves the Pimpernel and Armand so much that she betrays Chauvelin and France for them.
Though it is subtle, one can read from Chauvelin's character that he is also torn - between his thirst for glory for himself and his thirst for glory for France. That is why he does not tell Robespierre that he knows the identity of the Pimpernel - he wants the glory all for himself when he single-handedly captures the Pimpernel. He plans and carries out all these schemes for breaking Marguerite and killing the Pimpernel, and says it all for the good of France. But from his little sarcastic insults, manipulation, and twists, you can see that Chauvelin enjoys ruining people because he is egotistical and it makes him feel better.
So, the question the book asks is, what is more important? Loyalty to yourself and your morals, or your country and its morals?
Though it is subtle, one can read from Chauvelin's character that he is also torn - between his thirst for glory for himself and his thirst for glory for France. That is why he does not tell Robespierre that he knows the identity of the Pimpernel - he wants the glory all for himself when he single-handedly captures the Pimpernel. He plans and carries out all these schemes for breaking Marguerite and killing the Pimpernel, and says it all for the good of France. But from his little sarcastic insults, manipulation, and twists, you can see that Chauvelin enjoys ruining people because he is egotistical and it makes him feel better.
So, the question the book asks is, what is more important? Loyalty to yourself and your morals, or your country and its morals?