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is the fourth and final Sherlock Holmes novel by Arthur Conan Doyle, first published in 1915. The story begins with a mysterious murder at a country manor, investigated by Sherlock Holmes and Dr. Watson. The novel introduces a deeper conflict with Holmes’s archenemy, Professor Moriarty, and features an extended flashback that traces the roots of the crime to a violent secret society in America. Blending mystery, suspense, and drama, it is one of Doyle’s most complex and gripping works