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