When Nathan goes to visit his grandma, Nali, at her mobile summer home on the Navajo reservation, he knows he's in for a pretty uneventful summer, with no electricity or cell service. Still, he loves spending time with Nali and with his uncle Jet, though it's clear when Jet arrives that he brings his problems with him. One night, while lost in the nearby desert, Nathan finds someone extraordinary: a Holy Being from the Navajo Creation Story--a Water Monster--in need of help. Now Nathan must summon all his courage to save his new friend. With the help of other Navajo Holy Beings, Nathan is determined to save the Water Monster, and to support Uncle Jet in healing from his own pain.

Edward feels ready to move in with his dad's girlfriend and her son, Nathan. He might miss having his dad all to himself, but even if things in their new home are a little awkward, living with Nathan isn't so bad. And Nathan is glad to have found a new guardian for Dew, the young water monster who has been Nathan's responsibility for two years. Now that Nathan is starting to lose his childhood connection to the Holy Beings, Edward will be the one to take over as Dew's next guardian. But Edward has a lot to learn about taking care of a water monster. And fast. Because Dew's big sister, the powerful Yitoo Bii'aanii, is coming up to Fourth World to instruct Dew after recovering in the Third World for one hundred and sixty years. She suspects a monstrous and enormous Enemy from the Hero Twins stories has returned and is stealing water from all of the Navajo Nation. In their search for the Modern Enemy, Nathan, Edward, Dew, and Yitoo must confront their past and their inner selves if they are to save the Fourth World from a devastating disaster.