This is a story about magic and where it goes and perhaps more importantly where it comes from and why, although it doesn’t pretend to answer all or any of these questions.

It may, however, help to explain why Gandalf never got married and why Merlin was a man. Because this is also a story about sex, although probably not in the athletic, tumbling, count-the-legs-and-divide-by-two sense unless the characters get totally beyond the author’s control. They might.

However, it is primarily a story about a world. Here it comes now. Watch closely, the special effects are quite expensive.

A bass note sounds. It is a deep, vibrating chord that hints that the brass section may break in at any moment with a fanfare for the cosmos, because the scene is the blackness of deep space with a few stars glittering like the dandruff on the shoulders of God.

Then it comes into view overhead, bigger than the biggest, most unpleasantly armed starcruiser in the imagination of a three-ring film-maker: a turtle, ten thousand miles long. It is Great A’Tuin, one of the rare astrochelonians from a universe where things are less as they are and more like people imagine them to be, and it carries on its meteor-pocked shell four giant elephants who bear on their enormous shoulders the great round wheel of the Discworld.

As the viewpoint swings around, the whole of the world can be seen by the light of its tiny orbiting sun. There are continents, archipelagos, seas, deserts, mountain ranges and even a tiny central ice cap. The inhabitants of this place, it is obvious, won’t have any truck with global theories. Their world, bounded by an encircling ocean that falls forever into space in one long waterfall, is as round and flat as a geological pizza, although without the anchovies.