A Study in Scarlet is a detective mystery novel written by Sir Arthur Conan Doyle, introducing his new character of Sherlock Holmes, who later became one of the most famous literary detective characters. The book’s title derives from a speech given by Holmes to his sidekick Doctor Watson on the nature of his work, in which he describes the story’s murder investigation as his “study in scarlet”: “There’s the scarlet thread of murder running through the colourless skein of life, and our duty is to unravel it, and isolate it, and expose every inch of it.”

The Valley of Fear is the fourth and final Sherlock Holmes novel by Sir Arthur Conan Doyle. It is based on the supposedly real-life exploits of the Molly Maguires and Pinkerton agent James McParland. The story was first published in the Strand Magazine between September 1914 and May 1915, and the first book edition was published in New York on 27 February 1915.