Because there was a demented HOUND that had been tormented by Sir Henry's enemies to try to kill him. And, his enemies had stolen a shoe, Sir H's scent from which had been sniffed by the HOUND !!!! Dartmoor, UK, is a pretty desolate place when it's the 1800s and there's a hound hounding you. Even i you are the heir to "The Baskerville Fortune" ... Sir Arthur Conan Doyle, Sherlock Holmes and Dr Watson ....