The Sign of the FourThe Sign of the Four (also called The Sign of Four) is an 1890 detective novel, and is the second novel featuring Sherlock Holmes by Sir Arthur Conan Doyle. He also penned 56 short stories officially featuring Holmes and Watson, which were serialized and later collected in five volumes: The Adventures of Sherlock Holmes, The Memoirs of Sherlock Holmes, The Return of Sherlock Holmes, His Last Bow, and The Case Book of Sherlock Holmes.