I LOVED The Scarlet Pimpernell as a child (although I always thought the heroine, Marguerite(?), was more than a little dim for not guessing the Pimpernell's identity.)
This is wonderful reading - the dynamics have been set up so well, with the Revolution and Madame Guillotine as the impending threat, and Severus, and Sirius and Harry and the theatre, and even the Malfoys. It's fantastic - I can't wait to read the next chapter.