Mailliw's second adventure begins on Halloween. The joy of his friend Princess Frija's surprise visit is soon overshadowed by her terrible news. The black diamond has been stolen and her country is about to go to war with the Guardian of the Winter Mountains - the very person who had helped Mailliw to find a golden moonbeam in his first adventure. Despite the danger, Mailliw and friends have to do whatever it takes to prove the Guardian's innocence. To carry out their mission, they must go to Deep South - the home of the Goblins, the Vampire Cats and the ferocious Leatherback Clan. Their journey tests their courage and friendships, but will they succeed when they face enemies, have to take risks, and begin to discover the true power of the black diamond?