Monsterville is a village inhabited by monsters that have grown tired of living among humans. But one day, Hanna manages to break into her world by putting Monsterville at risk. After the initial fright, the monsters will have to fight against worse enemies: Gargoyle and Cyclops, two monsters that will want to use Hanna to permanently close any contact with the outside world ... running the risk of Hanna being trapped forever in Monsterville.

Hanna and the monsters come home for their first Christmas, only for Gargoyle's interference to erase it from memory. They team up with a little monster, Esna, on a quest to find the missing Spirit of Christmas and prevent Gargoyle and Cyclops from seizing power and saving Christmas.