Jack Pumpkinhead, a pal of the Oz Kids, who wants to take a boat ride with all of his friends. During the ride, the boat begins to sink and Jack and the Oz Kids enter the water. There they discover two mermaids who take them on a magical and adventurous underwater excursion. When Zog and the sea devils try to ruin their fun, the adventure gets more wild and exciting than Dot, Neddie and the Oz Kids ever expected.