The Sign of Four was the second novel featuring which famous fictional detective, following A Study In Scarlet?
Arthur Conan Doyle Sir Arthur Ignatius Conan Doyle KStJ, DL (22 May 1859 – 7 July 1930) was a British writer best known for his detective fiction featuring the character Sherlock Holmes. Originally a physician, in 1887 he published "A Study in Scarlet", the first of four novels about Holmes and Dr. Watson. In addition, Doyle wrote over fifty short stories featuring the famous detective.
Gareth Penn Gareth Sewell Penn (born 1941) is an American true crime author and amateur detective known for being among the first non-journalists to write about the Zodiac Killer case. He published a theory about the killer's motives, publicly accused a noted UC Berkeley public policy professor of the crimes, and labeled himself a one-time suspect.