Sir Arthur Conan Doyle’s “The Sign of the Four” (1890), is the second of four Sherlock Holmes novels, coming after “A Study In Scarlet” and before “The Hound of the Baskervilles”. In it, Holmes and Watson are enlisted by Mary Morstan to solve the mystery of her missing father who has recently returned from India. Compounding the mystery is the fact that she has received six pearls in the mail, one per year since 1882, from an anonymous sender. This complex mystery puts Holmes and Watson’s deductive skills to the test in a thrilling adventure involving poison darts and high-speed boat chases. First published in Lippincott’s Monthly, copies of the original magazine now fetch several thousand dollars in auction.