Celery Crumble is a very naughty girl who likes to play horrid tricks. But no matter how many times she is warned that if she behaves like a monster then a monster she will become, Celery just replies, 'Sorry. Not Sorry!' Until one morning Celery wakes to find she has boils on her back, claws on her toes, and a twitchy, stripy tail. Will Celery finally learn how to say sorry and curb her mischievous ways?