Sign of the four, the

The Sign of the Four, also called The Sign of Four, is the second novel featuring Sherlock Holmes written by Sir Arthur Conan Doyle. The Sign of the Four has a complex plot involving service in East India Company, India, the Indian Rebellion of 1857, a stolen treasure, and a secret pact among four convicts ("the Four" of the title) and two corrupt prison guards. It presents the detective's drug habit and humanizes him in a way that had not been done in A Study in Scarlet. It also introduces Doctor Watson's future wife, Mary Morstan. Sir Arthur Conan Doyle was a Scottish physician and writer, most noted for his stories about the detective Sherlock Holmes, generally considered a milestone in the field of crime fiction, and for the adventures of Professor Challenger. He was a prolific writer whose other works include science fiction stories, plays, romances, poetry, non-fiction and historical novels.