A Study In Scarlet, by Arthur Conan Doyle.

A Study in Scarlet is an 1887 detective novel by British author Arthur Conan Doyle. Written in 1886, the story marks the first appearance of Sherlock Holmes and Dr. Watson, who would become two of the most famous characters in popular fiction. The book's title derives from a speech given by Holmes, an amateur detective, to his friend and chronicler 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 (source: https://en.wikipedia.org/wiki/A_Study_in_Scarlet, 2016). Text extracted from The Project Gutenberg EBook of A Study In Scarlet, by Arthur Conan Doyle.