Cain the Caretaker tells the audience a Halloween tale about the House of Mystery where Batman, Zatanna, Constantine, and Doctor Fate are all turned back into 10-year-olds, with very little memory of who they really are, by Klarion the Witch Boy. After falling for Klarion's trap and regaining their memories, the 10-year-old Justice Leaguers must fight Klarion the Witch Boy even when he unleashes vampires, a werewolf, a monster that resembles Frankenstein's monster, a pumpkin-headed creature, and some small demons on them. They must also find a way to defeat Klarion when he gets his hands on the Helmet of Fate, turn themselves back to normal, and escape the House of Mystery before it disappears by midnight.