Their magic tree house takes Jack and Annie deep into the sea, where they meet up with dolphins, sharks, and octopi as they search for the answer to an ancient riddle.

Once an idyllic chain of inlets running from Key Largo to Key West, the Florida Keys have become an isolated universe of grotesquely mutated wildlife and bizarre submarine malformations. Blind seventy-foot sea snakes lurk among the reefs around underwater volcanoes, while typhoons and pirates turn the crystal waters above into a death zone. But Ryan Cawdor and his band of warrior-survivalists find a slice of heaven in this ocean hell at a marine research...