It's Sink or Swim for Jack and Annie when the Magic Tree House whisks them off to the middle of the ocean. Luckily, they find a mini-submarine on a coral reef. Unluckily, they are about to meet a giant octopus and one very hungry shark. Will the dolphins save the day? Or are Jack and Annie doomed to be dinner? You'll have fun finding out in... What do kids have to say about the Magic Tree House books? Look on the very first page! Read all the Magic Tree House books shown on the inside front cover.