Terrible horses

This little boy does not get on with his sister. They misunderstand each other, struggle to communicate, and they fight. Afterwards, there's a lot of hurt, heavy feelings and loneliness. In order to escape their constant rowing and clear his head, the boy often retreats to his bedroom when he writes his stories. He writes stories about terrible horses - trampling and galloping - and he, a lone pony, who cannot compete and cannot speak. But what happens when his sister finds his book? Could it be a way for them to finally understand each other?