Initials Only

A detective story first published in 1911, "Initials Only" deals with the case of beautiful young heiress Edith Challoner dropping dead in the writing room of a luxury hotel while nobody is near her, and no shot is heard and no bullet found in the deadly wound. Did she take her own life by stabbing herself through the heart with a paper knife, later found on the floor in the hotel lobby (but with no traces of blood on it)? Her grieving father refuses to believe the coroner's verdict of suicide, and employs an investigator who is actually part of the police force but acts on his own for most of the time. Among Miss Challoner's personal belongings are found letters signed with initials only, O.B. Who is O.B., and what - if anything - does he have to do with her death? Sweetwater, the investigator, finds out the identity of O.B. pretty soon, but instead of answering the questions the case poses, he only brings up more mysteries.