Maxwell is always in trouble. He's a total menace to his teachers and big sister, but has a soft side, too: he rescued his dog, Monster, from being run over and checks on his elderly neighbour after school. One day, while looking through a mysterious cabinet of curiosities, Maxwell finds himself erased from his life: it's as if he's never been born. At first, being able to walk around without being yelled at is great, but Maxwell starts to miss his old life. And, if he'd never existed, then he wouldn't have swooped Monster out of the path of that car.