The main character is a twelve-year-old boy named Wiley O'Mara. He lives on an island far up north where it is very cold, around the beginning of the nineteenth century. The island scenery and culture in some ways resemble that of Ireland around the same time. After meeting a dolphin who allows him to swim underwater, Wiley takes part in an extraordinary adventure through which he and the dolphin accomplish an incredible rescue mission. Along the way, Wiley and his friend encounter both real and imaginary creatures - the real fish, dolphins, coral reefs and changing depths of the North Atlantic Ocean, as well as imaginary creatures in the island forest and ocean depths surrounding Wiley's home.