This remarkable and acclaimed debut novel, by the Newbery-winning author of When You Reach Me and the new instant classic The List of Things That Will Not Change, introduces readers to a captivating, hidden world below the ice.    Peter is thrilled to join his parents on an expedition to Greenland. But when they finally reach the ice cap, he struggles to understand a series of frightening yet enticing visions.   Thea has never seen the sun. Her extraordinary people, suspected of witchcraft and nearly driven to extinction, have retreated to a secret world they’ve built deep inside the arctic ice.   As Thea dreams of a path to Earth’s surface, Peter’s search for answers brings him ever closer to her hidden home in this dazzling tale of mystery, science, and adventure at the top of the world.   “A mystic thriller.” —Entertainment Weekly   “Optimistic science fiction that highlights human ingenuity and survival under dire conditions.” —The Wall Street Journal