Question: The Sign of Four was the second novel featuring which famous fictional detective, following A Study In Scarlet?

Context articles: Lullaby (Atkins novel)
Sherlock Holmes Museum
Shock to the System (2006 film)
The Sign of Four (2001 film)
The Boy Sherlock Holmes
Arthur Conan Doyle
The Burglar and the Lady
The Gracie Allen Murder Case
Yellow Bird (company)
The Sign of the Four

Lullaby is the 41st novel featuring Robert B. Parker's fictional detective Spenser.
 It is the first official Spenser novel not written by Parker, but by Ace Atkins.
 Atkins was asked to write the novel after Parker's death in 2010.
The Sherlock Holmes Museum is a privately run museum in London, England, dedicated to the famous fictional detective Sherlock Holmes.
 It opened in 1990 and is situated in Baker Street, bearing the number 221B by permission of the City of Westminster, although it lies between numbers 237 and 241, near the north end of Baker Street in central London close to Regent's Park.
Shock to the System is a 2006 gay-themed mystery film.
 It is the second film adaptation of a Richard Stevenson novel featuring fictional detective Donald Strachey.
 The film premiered at the 2006 Outfest film festival before going into rotation on the here!
 television network.
The Sign of Four (2001) is a Canadian television film directed by Rodney Gibbons and starring Matt Frewer and Kenneth Welsh.
 The movie is based on Arthur Conan Doyle's second Sherlock Holmes story.
The Boy Sherlock Holmes series of novels, by Shane Peacock, are the childhood exploits of the famous fictional detective Sherlock Holmes.
 All are published by Tundra Books simultaneously in Canada and the U.S. (and appear in other countries and languages, including China, France, Vietnamese, Indonesia, and Spain).
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.
The Burglar and the Lady is a play written by Langdon McCormick.
 Like many of McCormick's plays, it was primarily a touring show and first premiered on October 1, 1905, at the State Street Theatre in Trenton, New Jersey.
 It came to Broadway in September 1906, appearing for a week at the American Theatre.
 The story pitted Sherlock Holmes, the famous fictional detective created by Arthur Conan Doyle, against A. J. Raffles, a fictional criminal created by E. W. Hornung.
 McCormick did not bother to ask permission for the use of either character.
 Former boxer "Gentleman Jim" Corbett played Raffles.
 The character's nationality was changed from English to American to match Corbett's casting.
 It was adapted as a movie in 1914, with Corbett again playing Raffles, although the adaptation removed the Holmes character.
The Gracie Allen Murder Case (1938) (also published as "The Scent of Murder") is the eleventh of twelve detective novels by S. S. Van Dine featuring his famous fictional detective of the 1920s and 1930s, Philo Vance.
 It also features the zany half of the Burns and Allen comedy team.
 It is in some ways a roman à clef, including not just Burns and Allen but also such characters as Gracie's mother and brother.
 (George Burns, after all, has described the couple's act as, "All I had to do was ask, 'Gracie, how's your brother?'
 and she talked for 38 years.")
 That gave the book an unusual feel, as did the comic tone of much of Gracie's dialogue.
 This tone suddenly shifts in a later chapter to one character's philosophically anguished speculations, and then back again to Gracie.
Yellow Bird is a Swedish film and television production company.
 In 2003 Danish producer Ole Søndberg and Swedish author Henning Mankell started a collaboration on a series of television films based on Mankell’s famous fictional detective Kurt Wallander and Yellow Bird was born.
 The success of the initial Wallander films was followed by Stieg Larsson’s worldwide phenomena, the Millennium trilogy, Jo Nesbø’s Headhunters, Liza Marklund’s Annika Bengtzon series as well as the British version of Wallander starring Kenneth Branagh.
The Sign of the Four (1890), also called The Sign of Four, is the second novel featuring Sherlock Holmes written by Sir Arthur Conan Doyle.
 Doyle wrote four novels and 56 stories starring the fictional detective.