After their adventures in the Jungle Biome, Stevie and Alex have tracked down another shard of the mysterious Ender crystal, which they must reassemble in order to keep the Ender Dragon from spawning in their world. With the new shard in hand, another segment of Alex's enchanted book becomes clear. Stevie and Alex are finally able to read the instructions for obtaining the next Ender crystal shard, and what they read amazes them. The book seems to want them to travel to a whole new biome--one that's underwater! But first, the friends will have to learn potion-making skills and adapt to fighting mobs in the water. There isn't much time, and the entire Overworld is depending on them. Can Stevie and Alex survive the unknown terrors of the underwater world in order to continue their quest to stop the terrifying Ender Dragon?