The Hound of The Baskervilles is my favourite Sherlock Holmes film, this one is from 1939 with Basil Rathbone as Holmes and Nigel Bruce as Dr. Watson.
The head of the Baskerville family dies under suspicious circumstances and when the last remaining heir, Sir Henry Baskerville (Richard Greene), arrives from Canada, there are several attempts on his life.
Centred around Dartmoor, Holmes finds the culprit, Stapleton, who also lives on the moor.
He is a distant relative and if Sir Henry dies, is next in line to inherit everything.