The six mermaids speed their way to the glowing underwater volcanoes where they plan to wrest the stolen Snow Diamonds from Mantora's clutches. Poppy, knowing she has one last chance to prove herself as a worthy Sister of the Sea, organises a courageous stand against Mantora and lifts her friends' spirits as they succeed in winning the precious Snow Diamonds back. However their adventures are not over until they have returned the Snow Diamonds to a casket in Ice Kingdom. They must combine the special magic from their Stardust Lockets to release Princess Arctica from an evil spell and restore Ice Kingdom to its former glory.