"The Sign of the Four" (1890) is Sir Arthur Conan Doyle's second novel featuring Sherlock Holmes and Dr. Watson. The story begins when Mary Morstan seeks their help regarding her missing father and mysterious gifts of pearls she received annually. As the investigation unfolds, they uncover a tale of stolen treasure, betrayal, and a pact made in India. The novel introduces Watson's future wife, Mary, and showcases Holmes's deductive prowess. Set against a backdrop of Victorian London, the narrative delves into themes of greed and justice, solidifying Holmes and Watson's partnership.