TERRY PRATCHETT finally succumbed in March to the Alzheimer’s that had been dogging his footsteps since 2007. The Shepherd’s Crown (Random House £20 (£18); 978-0-857-53481-1) is his last novel, and a farewell to the Discworld, the alternative universe that he had used to hold up a satirical mirror to our own for the past 30 years. Its starting-point is also a death, that of one of his major characters, Granny Weatherwax.

Witches don’t have a hierarchy, but, if they did, she might have been top. They can foresee their own deaths, and everything is left ready for her apprentice, Tiffany Aching, to take over her cottage and her role. It’s a big job, but Tiffany has the help of the Nac Mac Feegles, the six-inch-high tattooed Scotsmen, expelled from Fairyland for being drunk and disorderly.

Witches in Pratchett’s world take on the functions of the social services. They cut old men’s toenails and wash their clothes. “You do the good you see,” Tiffany says crossly to a more senior colleague who questions the dignity of such activities. They deal with people as they are, without judging them.

But, while Pratchett believes that his universe is good, he never forgets that parts of it are very black indeed. The elves, who practise “nastiness for the sake of being nasty”, are rallying to invade, and witches must gather to do real magic and fight them.

The prose is slightly calmer and slower than previously, with fewer jokes, but the sense of moral purpose is the same. Pratchett’s constant theme is that people are capable of change and growth. Even the Queen of the Elves discovers friendship and loyalty. Death, another favourite Pratchett character, who always talks in capital letters, tells Granny Weatherwax: “YOU HAVE LEFT THE WORLD MUCH BETTER THAN YOU FOUND IT” — which could stand as the author’s own epitaph.

Fiona Hook is a writer and EFL teacher.