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.

Sometimes the only way to hold onto what we love is to let it go.

Kai Sosa is so passionate about swimming he is practically a fish. This summer, he's determined to become the athlete he once was on an elite invitational team.

But something invisible holds him back. His race times are off. Dreams of his sister Cali haunt him. And he hasn't found her missing gold cuff, her last request. Mom is still talking about grief, even though it's been two years. He's fine now, isn't he?

When Kai discovers a library book Cali had checked out multiple times--about an underwater realm and a mysterious place called the Library of Despair and Sorrow--details from the story begin to appear in his own life: dolphin pods, imposing rock towers, unusual sea creatures, and even Cali's beloved bracelet. As myth and reality collide, El Niño unleashes its fury, and Kai is swept up in a storm of events that will change his understanding of love, death, grief, and how best to honor those we've lost.