Deep in the heart of a mist-shrouded island, an impossible secret is about to be discovered. Twig is used to feeling unwanted. Sent to live on a pony ranch for "troubled" girls on a misty, haunted island, Twig is about to discover the impossible — someone who needs her. Jolted awake from a bad dream, Twig follows the desperate whinny of a terrified horse out to the stables. There in the straw is a bleating little scrap of moonbeam. A silver-white filly with cloven hooves and a tiny, spiraling horn. A baby unicorn. Now Twig knows what secret is hiding in the island's mist: the last free unicorn herd. And a mysterious boy named Ben who insists that this impossible creature is now Twig's to care for. That she needs Twig's love and protection. Because there's something out there in the deep, dense shadows that's hunting for them.