The Sign of the Four is a classic Sherlock Holmes mystery by Arthur Conan Doyle, following Holmes and Dr. Watson as they investigate a strange case involving a missing father, a mysterious inheritance, and a hidden treasure. Their search leads through coded messages, secret agreements, murder, and a dramatic pursuit across London. Holmes relies on careful observation, scientific reasoning, and deduction to uncover the truth behind the crime. The novel also develops Watson’s personal story and introduces important elements of Holmes’s character. Fast-paced and atmospheric, it combines detective fiction, adventure, suspense, and intrigue in an enduring mystery.