Terry Pratchett was never so witty, direct and generous as in this, his final Discworld novelAll the best-loved authors, it seems, now leave a last book, to be published posthumously – Joan Aiken, Agatha Christie and (supposedly) Stieg Larsson, to mention just a few – and now, with The Shepherd’s Crown, it is the turn of Terry Pratchett, who died in March 2015.