On the moor I met Mr Stapleton, a naturalist with a butterfly net, who lived with his sister at Merripit House. He showed me the Grimpen Mire, a great green plain of bright grass where a false step meant death for man or beast. While we watched, a moor pony sank into it and was sucked down, screaming. Then a long, low moan swept over the moor, and Stapleton said the peasants called it the Hound of the Baskervilles calling for its prey. His sister was tall and beautiful and very unlike him. When he was out of hearing she spoke to me quickly. Go straight back to London, she said, instantly. She had taken me for Sir Henry, and when she learned her mistake she would say no more.