Dr. Mortimer, who has a general practice on Dartmoor, consults Holmes. His friend Sir Charles Baskerville has recently died, supposedly of a heart attack but Dr.Mortimer links the death to the myth of the hound of the Baskervilles, which, centuries earlier, killed wicked Hugo Baskerville and is said to haunt each generation. Sir Charles' young heir and nephew Henry is returning from abroad and the doctor fears for his safety. Sir Henry has a boot stolen from his hotel room and is followed by a bearded man. Holmes sends Dr. Watson off to Dartmoor with Mortimer and Henry, where he meets the butterfly collector and his sister Beryl, plus the very nervous housekeeper and valet to the Baskervilles, Mr. and Mrs. Barrymore, who appear to be signalling to someone on the moor...