The best time of the year has arrived-Mermicorn Island's annual costume contest. Lucky loves making ever more elaborate costumes for his Fintastic Four in the hopes of finally taking home the grand prize. When a fierce-looking shark crashes the ball, everyone swims for cover. Lucky's not sure that even one of his special seashells can save the celebration. But after the shark turns out to be more sweet than scary, Lucky is eager to extend a fin to help her. He knows better than any-fishy the importance of "sharing the magic."