The Magician's Nephew by C. S. Lewis, Clive Staples Lewis
Completed in February 1954 and published by Bodley Head in London on 2 May 1955, the prequel The Magician's Nephew brings the reader back to the origins of Narnia where we learn how Aslan created the world and how evil first entered it. Digory Kirke and his friend Polly Plummer stumble into different worlds by experimenting with magic rings made by Digory's uncle. They encounter Jadis (The White Witch) in the dying world of Charn, and witness the creation of Narnia. Many long-standing questions about the world are answered as a result. The story is set in 1900, when Digory was a 12-year-old boy. He is a middle-aged professor and host to the Pevensie children by the time of The Lion, the Witch and the Wardrobe 40 years later.