The Garza family's Christmas vacation in Mexico is cut short by the appearance of Pingo, one of the tzapame - Little People. The news is grim - a rogue prince from an ancient undersea kingdom is seeking the Shadow Stone, a device he will use to flood the world and wipe out humanity. Now Carol and Johnny must join a group of merfolk and travel into the deepest chasms of the Pacific Ocean to stop him and his monstrous army with their savage magic.