They go in the magic tree house to go on a very hard journey. And Morgan LeFay, she reached into her robe and pulled out a rolled up piece of paper. They had to solve the riddle. When they were at the reef, they found a mini sub. And Jack, he read "this is a coral reef".
They went in the mini sub and Annie made it go underwater. At the end they rode dolphins because the submarine was broken before they got back to the reef. It was too far to swim, and they got attacked by an octopus with ink and chased by a shark. The dolphins helped them escape.
