Book Description: Take the plunge with Jack and Annie!Jack and Annie continue their quest for the secrets of happinessâ€”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, theyâ€™re not sure who needs help moreâ€”Merlin or themselves! The brother and sister team are soon rescued by a ship of explorers and scientists. But that isnâ€™t the end of their troubles, because the crew isnâ€™t looking for the secrets of happiness. The crew is looking for . . . a sea monster!Mary Pope Osborne takes young readers back to the mid-nineteenth century, a time of exploration and adventure. This paperback edition contains all-new backmatter full of activities, and the first printing includes temporary tattoos.