The Red Thumb Mark by R. Austin Freeman

Richard Austin Freeman (11 April 1862 London - 28 September 1943 Gravesend) — known as R. Austin Freeman — was a British writer of detective stories, mostly featuring the medico-legal forensic investigator Dr Thorndyke. He claimed to have invented the inverted detective story (a crime fiction in which the commission of the crime is described at the beginning, usually including the identity of the perpetrator, with the story then describing the detective's attempt to solve the mystery) and used some of his early experiences as a colonial surgeon in his novels. A large proportion of the Dr Thorndyke stories involve genuine, but often quite arcane, points of scientific knowledge, from areas such as tropical medicine, metallurgy and toxicology.