Conan Doyle is the greatest writer of detective novels, and his legendary Sherlock Holmes series is the obvious "king". No other story could ever reach its iconic status, and even today, in 2017, BBC's Sherlock is breaking all kinds of records. As for The Valley of Fear, it's the 4th and final chapter in the franchise and was first released in 1914.
The book begins with Holmes receiving a cryptic message from Fred. But, he changes his mind soon after and fears that if the Professor learns of his treason, he'll be punished. So, he keeps the key to the cipher, and without it, Sherlock won't be able to access it. However, he does inform the detective of his decision. At the same time, Holmes is not one to sit on his hands, and he starts an investigation, hoping to crack the code.
He learns that the book for encryption is pretty common, fairly big, and standard in everything else. An almanac seems like the perfect fit for the description - the latest print of Whitaker's almanac doesn't match, though; the previous edition does! The message contains a warning that Douglas, a fine gentleman, is in danger.
But, before the detective gets a chance to help the poor fella out, Inspector Macdonald with the police department arrives in town and delivers the bad news: Mr. Douglas has just been murdered. Sherlock tells the man about the message and suggests that Moriarty is somehow involved. Yet, the inspector can't actually believe that someone like him would be connected to a murder case. So, now it's up to Holmes to figure out what really happened and why Moriarty wanted John dead. The Valley of Fear is a wonderful Sherlock Holmes detective novel and would be a great read for all the fans of the genre.