The Light Fantastic
Terry Pratchett's Discworld series continues with one of the few stories that is a direct sequel. The Light Fantastic takes up where The Colour of Magic left off, with Rincewind the wizard and Twoflower the tourist falling off the edge of the world. While certain death seems imminent, the powerful eighth spell of the Octavio, currently locked in Rincewinds' head, come forth to rescue Rincewind (and as a by-product, itself). Of course it's never that simple. When the spell surfaces, it also informs us that the destination of Great A'Tuin is rapidly approaching and it the eight great spells aren't spoken, the world will end. And here Rincewind was just coming to terms with Death (and Deaths adopted daughter, Ysabell).
As you can expect, as news of the approaching doom spreads, the population panics and religious chaos reigns. And to make matters worse, the wizard Trymon decides the time is right for him to gain the ultimate power. He decides to read the Octavio, and absorb the seven remaining great spells himself, and take charge of the Disc. You'll have to find out for yourself how this works out.
The movie I mentioned in the last post, The Colour of Magic (2008), by Sky One, combines the two novels into one movie, relating the full story in one sitting. Some of the smaller adventures get cut out, while building up on the character of Trymon.
"He moved in a way that suggested he was attempting the world speed record for the nonchalant walk." -- (Terry Pratchett, The Light Fantastic)