The Light Fantastic - Terry Pratchett

The Discworld is very much like our own - if our own were to consist of a flat planet balanced on the back of four elephants which stand on the back of a giant turtle, that is . . 'What shall we do?' said Twoflower. 'Panic?' said Rincewind hopefully. He always held that panic was the best means of survival. As it moves towards a seemingly inevitable collision with a malevolent red star, the Discworld could do with a hero. What it doesn't need is a singularly inept and cowardly wizard, still recovering from the trauma of falling off the edge of the world, or a well-meaning tourist and his luggage which has a mind (and legs) of its own. Which is a shame, because that's all there is . . .