His Dark Materials III: The Amber Spyglass (full-colour illustrated edition)

"The main conceit to know is that in this world, people have daemons. These are a sort of external soul in the form of an animal – a psychically linked companion that can never move too far from you. By adulthood, their form is fixed, but children’s daemons can shapeshift. This is central to the plot, but also massively central to the fantasy appeal. Reading it, you want a daemon so badly."