THE new Discworld book is about networks, intellectual property, eternal recurrence and Hope.

But above all it's about letters. In the teeming metropolis of Ankh-Morpork (itself one of Pratchett's most enduring creations), condemned fraud Moist von Lipwig is rescued from the scaffold on the condition that he reform the city's decayed Post Office. Delivering decades' worth of late post would itself be problem enough, but it is in the interests of the unscrupulous semaphore company that he fail.

In some ways, Going Postal is two books in one; an eerie tale of an office haunted by its post, and a searing attack on corporate corruption as exemplified by the Grand Trunk semaphore company. The two don't quite cohere, but nor does either aspect feel rushed or jarring, and far better a slightly disjointed book than two whose material was spread too thin.

In any case, even aside from the narrative, and Pratchett's hilariously wise authorial voice, there is a linking thematic thread; they're both stories about how organisations lose their way.

The book is presumably inspired by the failings of our own postal service and railways; by fury at profiteering, jargon-infected corporate cultures; by inquiries which always seem to absolve companies of blame for the blood on their hands.

The more literal-minded might have preferred Pratchett to write about our world directly, rather than in a fantastical mirror, but while such a book may have contained more facts, it would not have been so true.

Going Postal by Terry Pratchett (Doubleday, £17.99)