In "The Man with the Twisted Lip" by Arthur Conan Doyle, Sherlock Holmes investigates the mysterious disappearance of a respectable man last seen in a notorious opium den. Dr. Watson joins Holmes as they delve into the case, uncovering peculiar clues involving a disfigured beggar and a baffling case of mistaken identity. As the story unfolds, Holmes uses his keen deductive skills to unravel the truth behind the perplexing mystery.