In their fifth thrilling adventure, the explorers journey deep into the Bubble Ocean on their quest to stop the evil Collector, but time is running out . . . The Poison Tentacle Sea was home to the powerful Bone Current. As they had feared, it gave a sudden surge and pulled them in. Half-mermaid Ursula Jellyfin has always longed for adventure, and this time the stakes are higher than ever. The Collector is holding a group of children prisoner on Pirate Island, and it's up to Ursula and her friends Jai, Max and Genie to set them free. Armed with a magical mermaid trident, and with new recruit Zara the pirate fairy on board, their mission is filled with danger. The explorers must face zombie skeletons, make a daring rescue from a whirlpool and travel through a dinosaur graveyard. But even if they do make it to Pirate Island, can they fool the Collector and get in to an impenetrable fort?