Cain the Caretaker tells the audience a Halloween story about the House of Mystery, where Batman, Zatanna, Constantine, and Doctor Fate are turned into 10-year-olds by Klarion the Witch Boy. Now, the 10-year-old Justice League must find a way to defeat Klarion, turn them back to normal, and escape the House of Mystery before it disappears by midnight.

Stargirl has to enlist Constantine's help when Klarion the Witch Boy takes the place of the boy she's supposed to be babysitting...