The Valley of Fear is one of my favourite Sherlock Holmes novels, and second only to The Sign of Four - it's a cracking detective novel, a masterclass in how it's done by Sir Arthur Conan Doyle. This is Holmes at his best, in a format that's unusual and incredibly interesting when coupled with the genre.
See, the second half of the novel is set twenty years after the first half, in which Holmes is presented with an unusual case - he's asked to investigate the apparent death of a man called Douglas, who appears to have shot himself in the head with an American-style sawed-off shotgun.
However, not everything is as it seems, and the conclusion of Holmes' investigation leads you in to the second half of the adventure. That was the best part, following a young man named McMurdo through a giant conspiracy which, frankly, I don't have the time to talk about. Just grab a copy and read it yourself - I promise you won't regret it.