The Great Impersonation (1920). By

The Great Impersonation is a mystery novel written by E. Phillips Oppenheim and published in 1920. German Leopold von Ragastein meets his doppelganger, Englishman Everard Dominey, in Africa, and plans to murder him and steal his identity in order to spy on English high society just prior to World War I. However, doubts of the returned Dominey's true identity begin to arise in this tale of romance, political intrigue, and a (literally) haunting past.The story begins in German East Africa, where Englishman Everard Dominey awakens to his doppelganger host, German Leopold von Ragastein. They spend the night drinking and sharing their dark pasts. The next day, Leopold and Dr. Schmidt hatch a plan to make Everard disappear in the wilderness, thereby allowing Leopold to steal his identity and fulfill his special commission for the German government. In London, Everard seems very different from his peers, but is so familiar with his own past that he is accepted back. Unfortunately, his wife, Lady Rosamund Dominey, is still insane, and still thinks that Everard killed Roger Unthank, who disappeared just before Everard left and has not been seen since. Princess Stephanie Eiderstrom recognizes Everard as Leopold immediately, and threatens to reveal him if he does not meet with her later. Everard speaks with Mr. Seaman and reveals that Leopold killed a Hungarian prince, the husband of his lover the Princess Eiderstrom, which is why he was banished to Africa. He sends Seaman to the princess and lets her know that they cannot be together until he is done being Everard. Seaman, in turn, informs him that his true mission in England is to keep an eye on Ambassador Terniloff. Princess Eiderstrom informs Terniloff of Leopold's true identity. The Prince means to ensure that Leopold is a spy for peace, not warfare, and he assures the Prince that the former is true. At the Dominey estate, Mrs. Unthank accuses Everard of murder. Everard and her son, Roger Unthank, had fought over Lady Dominey soon before Everard left for Africa, and he hasn't been seen since. As a result, Lady Dominey wishes to kill her husband, and the ghost of Roger Unthank haunts the manor weekly. That night, Everard wakes up to his wife holding a knife to his throat, but she leaves. She summons him to her room the next day; she has lost her desire to kill him, but cannot figure out why. Everard goes to her doctor and he tells Everard that Mrs. Unthank is bad for Rosamund's health, and that her sanity depends on Everard's actions alone, now that he has returned. Rosamund is sent to a mental hospital. Mr. Seaman tells Everard that he has been asked to see Kaiser Wilhelm I in person. Everard confronts Mrs. Unthank and makes her leave the manor. In Germany, the Kaiser reminds Everard of Germany's intentions to start a war, insists that he stay close to Terniloff, and promises that if he succeeds in England, his banishment will be rescinded. Back in England, a hunting party is formed, and Terniloff finds out about the haunting of Roger Unthank. Princess Eiderstrom brings Everard a letter from the Kaiser, which both allows and insists that Everard marry her. He rejects her, both because it could possibly reveal his identity and because he secretly has feelings for Rosamund Dominey, who just returned from the mental hospital. Lady Dominey has one last remnant of her insanity left: she believes that the returned Everard is not really her husband. Everard and the hunting party explore Black Wood and find that the ghost has left tracks. Lady Dominey plays the role of hostess, finally returning to high society after over a decade of absence.... Edward Phillips Oppenheim (22 October 1866 - 3 February 1946) was an English novelist, in his lifetime a major and successful writer of genre fiction including thrillers.