The Sign of the Four (1890), also called The Sign of Four,  is the second novel in which we find investigator Sherlock Holmes as the protagonist.Miss  Mary Morstan hires Holmes because her father disappeared in India during an expedition. For years, the day of her  father’s disappearance, Miss Morstan receives a pearl as a gift. Meanwhile, the author of the gift had contacted her to meet her, so ‘the lady is accompanied to the meeting by Holmes and Watson … and from here begins the adventure and  the mystery.The most important work on Sherlock Holmes second great part of literary critics.