The Light Fantastic. Discworld Novel 2
'Panic?' said Rincewind hopefully. He always held that panic was the best means of survival. When the very fabric of time and space are about to be put through the wringer - in this instance by the imminent arrival of a very large and determinedly oncoming meteorite - circumstances require a very particular type of hero.Sadly what the situation does not need is a singularly inept wizard, still recovering from the trauma of falling off the edge of the world. Equally it does not need one well-meaning tourist and his luggage which has a mind of its own. Which is a shame because that's all there is...