What do you get when you combine Hitchhiker's Guide to the Galaxy, Dune and the Foundation trilogy? The answer is an interesting book by Terry Pratchett, entitled The Dark Side of the Sun. It was written in 1976, long before the first Discworld novels. On occasion it is evident that this was an early effort by Pratchett - it's not as funny or thoughtful as any of his later works, and it's very brief and hurried in places. But there's a lot of interesting ideas and concepts, show-casing the inventive mind of Pratchett in his early days. There are a number of ideas here (mostly just names) that will later turn up in the Discworld novels (for example, Hogswatchnight, Small Gods, etc.).
The story is about Dom Salabos, a member of the wealthy Salabos family in charge of the world of Widdershins. Dom should have the perfect life, but there is one problem: he keeps getting assassinated all the time. The story revolves around the concept of probability math, with Dom setting off on a quest to find the mysterious Jokers World, accompanied by his robot Isaac and his alien mentor Hrsh-Hgn. One thing to note is that there is no heroine or "love interest" in this book, refreshingly enough. However, just before the ending, it's as if Pratchett has noticed this short-coming, and a "female lead" type of character is introduced. The ensuing scenes jars violently with the preceding story, both in style and content, and it's as if you suddenly find yourself reading an entirely different story. The ending itself is very abrupt and hurried, and not very satisfying.
This book does show that Pratchett could be one of the sci-fi greats if he wanted to. However, much more could have been made with the universe and the ideas Pratchett developed in Dark Side, and it's to be hoped that he will return to the realm of sci-fi some day. Recommended for fans of Pratchett (and of sci-fi in general).