In this sequel to Bowles' Pura Belpré Honor Book The Smoking Mirror (2015), Carol and Johnny Garza are naguales, powerful shape-shifters, but before they have a chance to master their abilities, they set off on a new adventure to an undersea kingdom. Carol and Johnny will need to use their magic to help the merfolk and, once again, save humanity. This mission will require that they face their old nemesis, Tezcatlipoca, a dangerous Aztec god. Older middle-grade readers will enjoy reading about the Garza twins' unique adventures and about Mexico's rich mythology. Bowles creates an extraordinary world where the young characters have much to gain from their Mexican ancestry. Bowles provides a great "Guide to Pronunciation" that will help readers with Spanish and Nahuatl words. Other middle-grade books that allow their characters, and readers alike, to learn from Mexican culture include Xavier Garza's Maximilian & the Mystery of the Guardian Angel (2011) and Cathy Camper and Raúl the Third's Lowriders to the Center of the Earth (2016).