From the beloved, New York Times bestselling author of Esperanza Rising and Echo comes an enthralling aquatic adventure rippling with mystery and magical realism. Perfect for fans of Kate DiCamillo, Tae Keller, Jacqueline Woodson, and Meg Medina. Kai Sosa comes from a long line of competitive swimmers. And this is his summer to prove his own prowess on an elite invitational team, even if he is the weakest link. He hopes to carry the Sosa torch in a competition against the infamous Sea Wolves. But recently, he's been haunted by a puzzling dream. One where he sees his dead sister, Cali, swimming in the Pacific Ocean, surrounded by dolphins. When he wakes, it's hard to hold back the dam of feeling he's been working so hard to contain the past two years.

But he must, because feeling will mess with his race times. Then one day, while surfing with a friend, Kai encounters a mysterious sea creature as big as he, with long black hair and a fluked tail, that insistently pokes his board. Kai is sure his mind and the sea are playing tricks, until the sea creature finds Kai twice more. When a school assignment about the weather phenomenon El Niño leads him to the local library--and a book Cali had checked out multiple times, about dolphins and a mythic Amazonian queen who once ruled over an underwater realm--Kai's grip on reality begins to fissure. What are the sea creature and the book trying to tell him? In a climactic head-to-head faceoff with the Sea Wolves, everything becomes clear as Kai tests his strength, unleashes the dam, and discovers that sometimes the only way to hold onto what we love is to let it go.