"The Sign of the Four" is an exciting detective novel by the great writer Arthur Conan Doyle. This book tells us the story of the famous detective Sherlock Holmes and his faithful friend Dr. Watson, who together solve complex criminal cases in London at the end of the 19th century. In this book, the heroes embark on a dangerous adventure, uncovering the secrets of the past and following the trail of a mysterious crime. The Sign of Four is a gripping read that will keep you on the edge of your seat until the last page.