13 - Rupert of Hentzau by Anthony Hope

Rupert of Hentzau is the thrilling sequel to The Prisoner of Zenda, continuing the tale of political intrigue, romance, and adventure in the kingdom of Ruritania. When a treacherous nobleman obtains a secret letter that could destroy the monarchy, Rudolf Rassendyll must once again step into danger to prevent a crisis. A gripping novel filled with duels, deception, and high-stakes drama.