Siblings Mimi and Luke discover a powerful gemstone that grants total control over the imprisoned Archduke of Nightmares. Renamed Psycho Goreman by Mimi, the monster is forced into the rigid, petty hierarchy of the family home. As the creature summons his former army to Earth, the intergalactic warrior Pandora arrives to execute him. Tensions boil over when the children, their parents, and competing alien factions converge at an abandoned factory to decide the fate of the universe. The conflict forces the family to confront the corrupting influence of the gem while the entity balances his ancient thirst for destruction against a newfound, bizarre connection to his captors.