Obe Devlin has problems. His family's farmland has been taken over by developers. His best friend Tommy abandoned him for the development kids. And he keeps getting nosebleeds, because of that thing he doesn't like to talk about. So Obe hangs out at the creek by his house, in the last wild patch left, picking up litter and looking for animal tracks.

One day, he sees a creature that looks kind of like a large dog, or maybe a small boar. And as he watches it, he realizes it eats plastic. Only plastic. Water bottles, shopping bags... No one has ever seen a creature like this before, because there's never been a creature like this before. The animal - Marvin Gardens - soon becomes Obe's best friend and biggest secret. But to keep him safe from the developers and Tommy and his friends, Obe must make a decision that might change everything.