Magician's Nephew.

Digory let out a scream. “What's happened to Polly?” “Congratulate me, my dear boy,” said Uncle Andrew, rubbing his hands. “My experiment has succeeded. The little girl's gone – vanished – right out of this world.” When Digory and Polly discover Uncle Andrew's secret workshop, they are tricked into touching some magic rings that take them right out of this world. But even Uncle Andrew doesn't realise the wonders that lie ahead as they discover the gateway to the magical land of Narnia, where many thrilling adventures await them.