When Pat and Jen stumble into a hidden hole while playing hide-and-seek, they find that they're trapped in a dangerous underworld and that their good friend, Bomby, has been kidnapped! Now it's up to our daring duo and their "friend" Carter to battle the zombies, find the castle, and get back home before it's too late. Can Pat and Jen find Bomby and flee the underworld before they get zombified by the evilest villain of them all--Evil Jen?