The Sign of the Four is the second of Arthur Conan Doyle's Sherlock Holmes novels. In it the detective and his companion Dr Watson unravel 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.
Watson narrates the tale that sees the detective tracking down hidden treasure and murderers. By the end of the story the criminals are either dead or arrested, and Miss Mary Morstan and Watson are engaged to be married.