Sherlock Holmes receives a cipher message from Fred Porlock, an agent of Professor Moriarty. However, Porlock changes his mind for fear of Moriarty's discovering that he is a traitor and he decides not to send the key to the cipher, but he sends Holmes a note telling of this decision. From the cipher message and the second note, Holmes is able to deduce that it is a book-cipher. Holmes is able to decipher the message as a warning that "some devilry is intended against one Douglas", a country gentleman residing at Birlstone House. Some minutes later, Inspector Macdonald arrives at Baker Street with news that a Mr. John Douglas of Birlstone Manor House has been murdered. Holmes, Watson, and MacDonald travel to Birlstone House, an ancient moated manor house, to investigate the crime.

Arthur Conan Doyle (1859-1930) was a British writer best known for his detective fiction featuring Sherlock Holmes. The Sherlock Holmes stories are generally considered milestones in the field of crime fiction. Doyle is also known for writing the fictional adventures of Professor Challenger and for propagating the mystery of the Mary Celeste. He was a prolific writer whose other works include fantasy and science fiction stories, plays, romances, poetry, non-fiction and historical novels.