The Sign of the Four

When an Englishwoman receives mysterious gifts of pearls and a letter promising to right wrongs done to her, she calls upon Sherlock Holmes and Dr. Watson to investigate. <i>The Sign of the Four</i> has a complex plot involving service in East India Company, India, the Indian Rebellion of 1857, a stolen treasure, and a secret pact among four convicts ("the Four" 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 <i>A Study in Scarlet</i>. It also introduces Doctor Watson's future wife, Mary Morstan.