A classic detective novel by Arthur Conan Doyle and the second full-length adventure featuring the legendary detective Sherlock Holmes and his companion Dr. John Watson.

The story begins when Mary Morstan seeks Holmes's help regarding a mysterious annual gift of pearls and the disappearance of her father years earlier. The investigation leads Holmes and Watson into a complex mystery involving a hidden treasure, murder, betrayal, and a secret pact known as "The Sign of Four."

As Holmes follows a trail of clues across Victorian London, the case unfolds into an exciting adventure involving stolen riches, revenge, and one of the detective's most memorable investigations. The novel also develops Watson's personal life, introducing a romantic subplot that becomes important in later stories.