The Hound of the Baskervilles. The Valley of Fear

This collection included two Konan Doyla novels about the adventures of the Immortal tandem with Baker Street, 221-b,-the great detective of Sherlock Holmes and his friend and assistant Dr. Watson.
"Dog of Baskerville" is probably the most famous of the works about Sherlock Holmes. For the second century, all new generations of readers with unchanged enthusiasm and hobby have been monitoring the investigation of a case of a cruel crime, which is sophisticatedly disguised as a mysterious legend of a demonic dog, which has been pursuing an ancient aristocratic clan for the terrible deeds of one of his representatives ...
"Valley of horror" is a novel, which was published quite rarely in our country. However, it has special originality, because this is almost the only work about Sherlock Holmes, written on the basis of real events.
So, a certain Mr. Douglas is killed in his estate - the police think. Holmes is sure: the victim is not Mr. Douglas, but a man who was going to deal with him. But for what? And where and why did the owner of the house himself disappear?