During the reign of the Vikings, a man from another world crash-lands on Earth, bringing with him an alien predator. The man must fuse his advanced technology with the weaponry of the vikings to fight the monster.

The Cromwell clan live in the real world, except for their grandmother who lives in Halloweentown, a place where monsters go to escape reality. But now the son of the Cromwells’ old enemy Kalabar has a plan to use the grandmother’s book to turn Halloweentown into a grey dreary version of the real world, while transform the denizens of the real world into monsters.