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.