Sir Arthur Conan Doyle's second novel starring the great detective Sherlock Holmes, The Sign of the Four weaves together a complex plot involving stolen treasure, a secret pact between guards and prisoners, and the Indian Rebellion of 1857. Revealing and humanizing Holmes beyond his portrayal in A Study in Scarlet, this novel from 1890 shows us the detective's drug habits and introduces Watson's wife-to-be, Mary Morstan.