In London, weird things happen to Henry: he gets a note warning him not to come to the mansion, two of his shoes are stolen, and a bad guy follows him. Watson notices strange things going on in the mansion.
Watson gathers clues and writes reports to Holmes. Holmes is pretty sure the killer is Jack who used the legend of the ghostly, killer dog to scare Charles to death. Holmes is sure Jack has something up his sleeve to do away with Henry.
It turns out, Jack is really Henry's uncle, though he keeps his mouth shut about it, so no one will know he is out to get the Baskerville money and mansion. And Beryl is really his wife. Jack used a real-live dog dabbed with glow-in-the-dark paint to scare Charles to death. Jack was the bearded man trailing Henry through London. He stole Henry's shoe to give the dog his scent. Jack also locked Beryl in her HOTEL ROOM, but she figured out a way to send Henry a warning to stay away from the mansion.
Finally, Jack lures Henry to his house at night, and when Henry is walking home, Jack sicks his mad-dog after him. Holmes shoots the dog in the nick of time and chases Jack into a swampy maze of quicksand, where Jack falls and sinks to his death.