The Magician's Nephew (The Chronicles of Narnia, Bk 1) by C.S. Lewis

The Magician's Nephew tells the story of the creation of Narnia, and paves the way to understand how the rest of the series plays out.  We learn of the Sons of Adam and the Daughters of Eve, how the wardrobe came to be, and more. Digory and Polly are tricked by Digory's peculiar Uncle Andrew into becoming part of an experiment, they are set off on the adventure of a lifetime. What happens to the children when they touch Uncle Andrew's magic rings is far beyond anything even the old magician could have imagined.