The Sign of the Four is the second novel by Arthur Conan Doyle about master detective Sherlock Holmes and his partner Dr John Watson. In this story they solve a mystery of hidden treasure and murder.Miss Mary Morstan arrives at 221B, Baker Street to request help with the mystery of her missing father, her anonymous gifts of pearls and a letter requesting her to meet an unknown person that evening. Holmes takes on her case and the adventure begins.The story is set in 1888. The Sign of the Four has a complex plot involving service in India, the Indian Rebellion of 1857, a stolen treasure, and a secret pact among four convicts ("e;the Four"e; 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 the preceding novel, A Study in Scarlet (1887). It also introduces Doctor Watson's future wife, Mary Morstan.