When Rio is sent to live with a grandmother he barely knows in California, he feels completely alone. Then he makes a new friend on the foggy beach--a girl named Marina, who teaches him about the massive grey whales that migrate nearby.

As Rio grows to love the whales, he discovers that his mother loved them, too. He's suddenly sure that if he can somehow find a way to connect her with these gentle giants - and especially with a particular whale named White Beak - she will get better and come to join him in California. But White Beak is missing--and Rio must embark on a desperate journey across the dangerous ocean to find her.