An enthralling aquatic adventure rippling with mystery and magical realism from the beloved, New York Times bestselling author of Esperanza Rising and Echo. Perfect for fans of Kate DiCamillo, Tae Keller, Jacqueline Woodson, and Meg Medina.

During a summer of El Niño weather conditions, Kai Sosa hopes to prove his swimming prowess on an elite invitational team. Once an up-and-coming athlete, he is determined to live up to his family's swimming legacy in a competition against the infamous Sea Wolves, even if he is the team's weakest link.

But recently, he's been haunted by puzzling dreams where he sees his dead sister, Cali, swimming in the Pacific Ocean with dolphins. When he wakes, it's hard to hold back the dam of feeling he's been working so hard to contain. He becomes convinced Cali's sending him a message about her last request-to find a beloved gold cuff that went missing.

When Kai finally finds the elusive bracelet, it leads him to the local library-and a book Cali had checked out multiple times about a mythic mermalien queen of the same name, who once ruled over an underwater realm. Then, while surfing, Kai encounters an unusual sea-creature, as big as he, with long black hair and a fluked tail. Could it be the creature from the myth, or are Kai's mind and the sea playing tricks? In a climactic head-to-head face-off 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.