This novel is an exciting fusion of a Sherlock Holmes mystery with the Ruritanian world of intrigue and skulduggery of Anthony Hope's novel 'The Prisoner of Zenda'. Colonel Sapt of the Ruritanian Court journeys to England on a secret mission to save his country from anarchy. He is to engage the services of Rudolf Rassendyll once more to impersonate the King while the monarch recovers from a serious illness. But Rassendyll had mysteriously disappeared. In desperation Sapt consults Sherlock Holmes who with Watson travels to the Kingdom of Ruritania in an effort to thwart the plans of the scheming Rupert of Hentzau in his bid for the throne.