The Silver Chair

Shipped off to a miserable school, Eustace finds companionship in Jill Pole. Running from bullies, the two hide in a garden shed that magically transports them into the magical world of Narnia, where they're entrusted with a task by Aslan: to rescue the king's stolen son, Prince Rilian. Together, with Puddleglum the Marshwiggle, Eustace and Jill must travel north across the mountains, dodge giants, and journey down into the earth itself to rescue Rilian from the mysterious evil that holds him bound there.