First published in 1890, The Sign of Four is Sir Arthur Conan Doyle's second book starring legendary detective Sherlock Holmes. The story is complex, involving a secret between four ex-cons from India and a hidden treasure. More complex than the first Holmes novel, The Sign of Four also introduces the detective's drug habit and leaves breadcrumbs for the reader that lead toward the final resolution. Readers are offered an explanation of the mystery from the killer's perspective, encouraging a sense of sympathy with the condemned that the previous book also lacked. Any fan of the mystery genre should consider this book a must-read. Scottish surgeon and political activist SIR ARTHUR CONAN DOYLE (1859-1930) turned his passions into stories and novels, producing fiction and nonfiction works sometimes controversial (The Great Boer War, 1900), sometimes fanciful (The Coming of the Fairies, 1922), and sometimes legendary (The Adventures of Sherlock Holmes, 1892).