In Arthur Conan Doyle's novel The Hound of the Baskervilles, Sherlock Holmes is engaged by Dr. Mortenson to solve one murder, that of Sir Charles Baskerville, and prevent another, that of his young heir Sir Hugo Baskerville. He finds several features of the case intriguing, including the family legend of the mysterious, quasi-demonic hound, which has, according to local legend, haunted the family for generations. Rather than heading down to Baskerville Hall, Sherlock Holmes sends Dr. Watson in his stead, staying behind to investigate the identity of a mysterious man who has been spying on Sir Hugo Baskerville while Sir Hugo was in London, and a case of blackmailing. Holmes requests detailed reports from Dr. Watson.
Dr. Watson manages to solve a lesser mystery, the subplot concerning the escaped murderer Seldon, discovering that he is, in fact, the brother of Eliza Barrymore, the housekeeper and wife of the butler, and that she has been supplying him with food and clothing and arranging for him to leave England in secret. The greater mystery and the threat to Sir Hugo's life remain for Holmes to solve.
When Watson locates Holmes on the moor and requests an explanation of Holmes' secrecy, Holmes gives three reasons for it.
1. By staying on the moor rather than in the manor he can get a perspective different from that of the inhabitants of the manor and of Watson. He states:
Had I been with Sir Henry and you it is confident that my point of view would have been the same as yours.
2. He does not want to alert the criminals to his presence. He states:
... [M]y presence would have warned our very formidable opponents to be on their guard.
3. He was also concerned that Watson, knowing of his presence, might have endangered himself by visiting unnecessarily.