Batman teams up with John Constantine, Zatanna, and Swamp Thing when Solomon Grundy tries to raise a zombie army

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.