Terry Pratchett's profoundly irreverent novels are consistent number one bestsellers in England, where they have garnered him a revered position in the halls of parody next to Mark Twain, Kurt Vonnegut, Douglas Adams, and Carl Hiaasen.

In The Light Fantastic only one individual can save the world from a disastrous collision. Unfortunately, the hero happens to be the singularly inept wizard Rincewind, who was last seen falling off the edge of the world...

The sun rose slowly, as if it wasn't sure it was worth all the effort.

Another Disc day dawned, but very gradually, and this is why.

When light encounters a strong magical field it loses all sense of urgency. It slows right down. And on the Discworld the magic was embarrassingly strong, which meant that the soft yellow light of dawn flowed over the sleeping landscape like the caress of a gentle lover or, as some would have it, like golden syrup. It paused to fill up valleys. It piled up against mountain ranges. When it reached Cori Celesti, the ten mile spire of gray stone and green ice that marked the hub of the Disc and was the home of its gods, it built up in heaps until it finally crashed in great lazy tsunami as silent as velvet, across the dark landscape beyond.

It was a sight to be seen on no other world.

Of course, no other world was carried through the starry infinity on the backs of four giant elephants, who were themselves perched on the shell of a giant turtle. His name-or Her name, according to another school of thought-was Great A'Tuin; he-or, as it might be, she-will not take a central role in what follows but it is vital to an understanding of the Disc that he-or she-is there, down below the mines and sea ooze and fake fossil bones put there by a Creator with nothing better to do than upset archaeologists and give them silly ideas.

Great A'Tuin the star turtle, shell frosted with frozen methane, pitted with meteor craters, and scoured with asteroidal dust. Great A'Tuin, with eyes like ancient seas and a brain the size of a continent through which thoughts moved like little glittering glaciers. Great A'Tuim of the great slow sad flippers and star-polished carapace, laboring through the galactic night under the weight of the Disc. As large as worlds. As old as Time. As patient as a brick.

Actually, the philosophers have got it all wrong. Great A'Tuin is in fact having a great time.

Great A'Tuin is the only creature in the entire universe that knows exactly where it is going.

Of course, philosophers have debated for years about where Great A'Tuin might be going, and have often said how worried they are that they might never find out.

They're due to find out in about two months, And then they're really going to worry ...

Something else that has long worried the more imaginative philosophers on the Disc is the question of Great A'Tuin's sex, and quite a lot of time and trouble has been spent in trying to establish it once and for all.

In fact, as the great dark shape drifts past like an endless tortoiseshell hairbrush, the results of the latest effort are just coming into view.

Tumbling past, totally out of control, is the bronze shell of the Potent Voyager, a sort of neolithic spaceship built and pushed over the edge by the astronomerpriests of Krull, which is conveniently situated on the very rim of the world and proves, whatever people say, that there is such a thing as a free launch.

Inside the ship is Twoflower, the Disc's first tourist. He had recently spent some months exploring it and is now rapidly leaving it for reasons that are rather complicated but have to do with an attempt to escape from Krull.

This attempt has been one thousand percent successful.

But despite all the evidence that he may be the Disc's last tourist as well, he is enjoying the view.

Plunging along some two miles above him is Rincewind the wizard, in what on the Disc passes for a spacesuit. Picture it as a diving suit designed by men who have never seen the sea. Six months ago he was a perfectly ordinary failed wizard. Then he met Twoflower, was employed at an outrageous salary as his guide, and has spent most of the intervening time being shot at...

Terry Pratchett's novels have sold more than forty-five million (give or take a few million) copies worldwide. He lives in England.