The inestimable Mr Terry Pratchett seems to make a habit of churning out books every six months. The last one was Monstrous Regiment, and here we are in May with the latest installment "A Hat Full of Sky".

It's a direct follow-on from "The Wee Free Men", and features many of the same characters, not least of whom are the Nac Mac Feegle, who are the sort of lovable yet ultimately destructive Pictsies you wouldn't want to meet in a dark alleyway. But the true star of the show is Tiffany Aching, now eleven years old and under proper supervision to become a real witch. Other familiar characters are also involved - most notably Granny Weatherwax, the ancient crone and quite possibly the most powerful witch of all time.

This latest book is again apparently aimed at children. It's somewhat shorter that most of the recent Discworld books, and has a much younger central character. However, that's not to say that the flashes of imagination are any less, nor the plot any simpler. Pratchett has a great way of writing for a younger audience without forgetting that many of his older fans will be reading the story, and as such there is a strong moral core to the book that's as relevant if you're fifty as fifteen.

The plot twists and turns, managing to continue on after a lesser author would have allowed it to finish. It's also extremely funny, mixing jokes about types of people and rural living with some somewhat sharp and pointed barbs towards people who take themselves far too seriously. And the clearest point of all is made by Granny Weatherwax herself: "Wands and potions and rituals is easy. Being a witch is about people. And that's hard."

Hat Full of Sky is yet another worthy addition to the Discworld series, and deserves to be read by all - not just children, not just Pratchett fans, but everyone that likes a good tale.