"The Sign of the Four" is a detective novel written by Arthur Conan Doyle, featuring the famous detective Sherlock Holmes and his friend Dr. John Watson. The story revolves around a mysterious pact made by four convicts and a hidden treasure, which leads to a complex investigation in Victorian London. The plot begins when Mary Morstan seeks Holmes's help to uncover the truth behind her father's disappearance and the annual gifts of pearls she has received. As Holmes and Watson delve deeper, they encounter themes of loyalty, betrayal, and the quest for justice, culminating in a thrilling conclusion.