Rupert of Hentzau

Three years after Zenda: the queen's letter is in the wrong hands, Rupert of Hentzau is back in Ruritania, and the Englishman who once impersonated a king is asked to do it again — for a stake that cannot be given back. Hope was a barrister who thought up Zenda walking home from a court case and wrote it in a month; this sequel is the better book, and he had the nerve to give it the ending the first one avoided.