The Sign of Four is the second novel by Doyle about the exploits of Sherlock Holmes. From the moment that Mary Morstan tells Holmes about the mysterious disappearance of her father and the yearly gift of a pearl from an unknown benefactor, Holmes, and his companion Watson, are involved in an exotic tale of stolen treasure, secret oaths and murder, culminating in a breathtaking chase down the Thames. Holmes is in top form, and Watson fails in love.