The Magician's Nephew by C. S. Lewis

The adventure begins Narnia ... where Talking Beasts walk ... where a witch waits ... where a new world is about to be born. On a daring quest to save a life, two friends are hurled into another world, where an evil sorceress seeks to enslave them. But then the lion Aslan's song weaves itself into the fabric of a new land, a land that will be known as Narnia. And in Narnia, all things are possible ...