After taking a break from their trips in the tree house, Jack & Annie are delighted to find that it&8217;s back! Morgan le Fay needs their help &8211; but they&8217;ll have to become Master Librarians first, & that means solving four tricky riddles. For the first one, Morgan sends them deep into the middle of the ocean. Jack & Annie ride in an amazing mini-sub, meeting jellyfish, sea horses & an octopus! But there are some very scary sharks down there. Will a troupe of friendly dolphins come to the rescue&8230;?