A Hat Full of Sky by Terry Pratchett

All the fun of the fairies

For a while, the estimable Terry Pratchett divided his time between writing the Discworld series of comic fantasies for notional adults, and unrelated novels "for younger readers". Of late, perhaps mindful that his readers young and old tend not to make the same distinctions, he has been erasing demarcation lines. A Hat Full of Sky, a sequel to The Wee Free Men, has "a story of Discoworld" on the cover but is identifiable as a supposed children's book mostly by the fact that it has 11-year-old Tiffany Aching as protagonist.

One of the features of all Pratchett's work is the co-opting (and subversion) of a manner of authorial voice, at once confiding and superior, typical of old-fashioned children's books (E Nesbit comes to mind). Here, that same voice speaks a little more directly, perfectly suited to reading aloud, but retains its satiric cocked eyebrow. Occasionally, he feels the need to take several runs at a joke (one about hermit elephants never does quite come off) but, for the most part, you get the pure joy of gag-happy invention.

The "high concept" of the earlier book was the Nac Mac Feegle, a band of good-hearted but dangerous fairies who talk like Glaswegian football hooligans or really dim cast-outs from an Iain Banks book, but mind their manners when their mum is about. The Nac Mac Feegle return here, as do some favourite characters, but there's a sense that this is a Discworld book mainly because, for the plot, Pratchett needs some people (Granny Weatherwax, Death) already established as residents.

Otherwise, we're in a small, sheep-farming corner of a pocket universe ("the Chalk") that might as well be Wessex. The main attraction is a decent plot about a young witch targeted for possession by an ancient, bodiless spirit called a hiver (along the lines of Guy de Maupassant's horla). A great Pratchett strength is the sense that if the jokes (and the wonderfully recognisable British comic supporting characters) were dropped, there would still be a good, engaging fantasy thriller here.

The hiver's possession method is intriguingly unusual. Once it's in your mind, it thinks it is you, but in an increasingly paranoid, mean-spirited manner. The closet New Wave science-fiction writer in Pratchett relishes the Nac Mac Feegle's trip into the possessed heroine's mindscape - to give evil a good kicking.

After the story tangle is unthreaded there are still several chapters. These deliver a sustained comic set-piece about "witch trials" that aren't like the ones in real history (think sheepdog trials, or a village fête). Pratchett offers an affecting, beyond-good-and-evil resolution to the arc of the hiver, which makes young Tiffany a heroine of substance.

Kim Newman's latest novel is 'Dracula Cha Cha Cha' (Pocket)