Set 10 years after the events of The Horse Whispererer, HW is starting to lose his superhuman Horse Whispering ability. The horses can't hear him anymore so he has to keep talking louder and louder until eventually he's just yelling in their ears. But he's yelling so loud that it scares the shit out of the horses and they keep running away from him. Then, one tragic September morn, he yells "RUN REALLY FAST" in Billy the Horse's ear so loud that Billy kicks him in the fucking spine, paralizing him from the spine down. So now he has to chain the horses to the floor of a soundproof booth while he yells at them, otherwise they won't do what he commands. One day while sitting in his wheelchair naked in a soundproof booth yelling his lungs out at a chained-down horse, he's like "what have I become?" then he shoots himself in the head. But nobody hears the gunshot because he's still in the soundproof booth! By the time someone finds him, the horse has eaten most of his body. The End.
...or is it? After the credits, the horse that ate the Horse Yeller looks at the camera and its eyes glow red. The End????