My idea is this:

The story starts out explaining what a hellhound is. After that, it introduces a golden retriever named Chi. She and her owners are driving from texas to California to move because they couldn't afford a plane ticket. Te car breaks down in a bad town and a seemingly kind old man offers for them to stay at his place for the night because the sun is already setting. They accept and he begins making dinner for them. At first Chi doesn't trust the old man, but then she starts to change her mind about it. By the time Chi has fully trusted him, the family is amost done with their meal. While they're asleep, te man ambushes them while Chi tries to protect them. She fails, and two other men shoot the parents dead and the old man snaps their young daughter's neck. One of them knocks out chi with a bat and she is taken deep into a forest where she is put in a dog fight. As she is about to win, a man who bet Chi would lose throws a rock at her to distract her, allowing ehr opponent to rip at her neck so her head is halfway attatched to her neck. One of the men decides it would be funny to tie a rope around chi's neck and hang her from a tree, so he gets eight other men to come with im and they do so. Chi's head is ripped off from the weight of her body and she is beheaded while owling in pain. She wakes up and, upon realising she was dead, Chi is filled with anger and killing intent, so much that she becomes a hellhoud and beheads all 20 of the dog fighters. She then sets a goal to behead as many humans as she can.