Jack and Annie continue their quest for the secrets of happiness-secrets they need if they`re going to save Merlin. But when the magic tree house leads them to a tiny deserted island in the middle of the ocean, they`re not sure who needs help more-Merlin or themselves! The brother and sister team are soon rescued by a ship of explorers and scientists. But the crew isn`t looking for the secrets of happiness. The crew is looking a sea monster!