A Study in Scarlet

A Study in Scarlet is a detective novel by British author Arthur Conan Doyle. Published in 1887, the story marks the first appearance of Sherlock Holmes and Dr. Watson, who would go on to become one of the most well-known detective duos in literature.
The book's title derives from a speech given by Holmes, a consulting 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."
The story, and its main characters, attracted little public interest when it first appeared. Conan Doyle wrote 56 short stories featuring Holmes, A Study in Scarlet is the first of only four full-length novels in the original canon. It was followed by The Sign of the Four, published in 1890.
A Study in Scarlet was the first work of detective fiction to incorporate the magnifying glass as an investigative tool.