The Valley of Fear is a novel that involves puzzles, murder, and Professor Moriarty.  Holmes does not learn of Moriarty’s involvement until the end.  He just knows that he gets a message written in code than a man named John Douglas is about to be murdered.  Shortly after, Inspector MacDonald arrives to tell Holmes that it has happened.

Holmes now has his interest peaked.  Once at Douglas’s house, things get interesting. For one thing it is surrounded by a small moat.  There is a body they assume is Douglas.  Also, the wedding ring is missing, and there is a note left behind with “initials V.V. and under them the number 341.“  They realize someone has been hiding there.

It turns out that the body was not Douglas at all.  Douglas shot someone who broke into his house, and that is the body they found.  Douglas knows the man is a member of the “Vermissa Valley” gang from America.  We are then treated to a flashback explaining what happened in Vermissa Valley in 1875.

Douglas used to be called Birdy Edwards, and had a detective agency in Chicago, The Pinkerton National Detective Agency, run by the Ancient Order of Freemen.  He was investigating the gang for counterfeiting.  He changed his name to get away from them.

Douglas is acquitted, but later Holmes gets a note saying he has been killed.  He knows there is more to it.

"There is a master hand here. It is no case of sawed-off shotguns and clumsy six-shooters. You can tell an old master by the sweep of his brush. I can tell a Moriarty when I see one. This crime is from London, not from America." (epilogue)

Holmes is aware that Moriarty is going to be more trouble for him, and in fact Moriarty will be the nemesis that almost does him in.