The Sign of the Four, is the second novel featuring Sherlock Holmes. It has a complex plot involving service in East India Company, the Indian Rebellion of 1857, a stolen treasure, and a secret pact among four convicts and two corrupt prison guards. It also introduces Doctor Watson's future wife, Mary Morstan. Sir Arthur Ignatius Conan Doyle was a Scottish physician and writer, best known for his Sherlock Holmes detective stories and for the adventures of Professor Challenger. He was a prolific writer whose works include science fiction stories, plays, romances, poetry, non-fiction and historical novels.