It's Cookie Monster's first day at a new school and she's feeling nervous. Little does she know that this isn't a normal school. Not at all, her teacher is a witch, the librarian is a skeleton and what is wrong with the Principal and his evil laugh? After being punished with slime, bullies, custard pies and being chased by hippos Cookie Monster needs to find a way to get this Horror School closed down. With the help of her friends she comes up with a plan, but with Halloween approaching the ghosts are out to stop her and she's going to have to summon all her bravery to defeat the maniac Principal Brown.