We cannot write your assignment for you, but if we give you some ideas, you should be able to come up with a page of writing.
I have always thought that it was less than satisfying to have Stapleton fall over the cliff in his hideout at Great Grimpen Mire. Don't you think you could write a much scarier ending by extending the gothic qualities of this novel by not having the hound meet his demise by being shot by Holmes and Watson and perhaps turning on Stapleton? It would be poetic justice. You could invent some way that the hound would have wanted to pursue Stapleton. Let's say that he has also stolen a jacket that belonged to Sir Henry, not just his boot. Let's say that Stapleton was wearing the jacket when he excaped to the Mire. The hound breaks loose from his fetters and, following the scent that he thinks is Sir Henry's, he pursues Stapleton to the Mire.
You can create some gothic drama. Have Stapleton sitting before a fire on the Mire. He is trying to keep warm and eating some beef jerky. He hears an eery howl from far away. No big deal, he tells himself. It is probably some stray dog that has wandered onto the Mire. But the howling gets louder. And closer. And soon, he hears rustling of leaves and twigs. He gets up to investigate. Nothing. He starts to hear the heavy breathing of an animal. He looks around. Nothing. Suddenly, he sees two bright yellow orbs right in front of his face. He then smells a hideous odor. He then comes face to face with the hideous beast. The beast bears his teeth and attacks, jumping on Stapleton and tearing his jacket to pieces, then tearing out his throat, just as in the legend of the Hound of the Baskervilles of long ago.
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