A study in Scarlet is Sir Arthur Conan Doyle's first Sherlock Holmes adventure, a novel wherein much of the action takes place in the American West.  We are first introduced to John H. Watson, M.D., Late of the Army Medical Department.  Seeking a roommate, he is introduced to Sherlock Holmes.  The second chapter is an introduction to Holmes's Science of Deduction. Sherlock is invited to the scene of the crime in the third chapter by Scotland Yard detective Tobias Gregson, Lestrade is also present at the scene of the crime.