Pratchett puts his own stamp on the much-used plot by means of his Discworld machinery and his gift for comedy. On a planet where magic works, Esk can turn her brother into a pig — literally. She can get into more trouble than any Earth child; she can wreck a whole landscape when she has a tantrum. Granny Weatherwax can keep up with her only because she can do magic too, although her mishaps when she has to ride a broom — a trick she normally despises — are among the funniest moments in the book. Fantasy can be a fresh and extraordinary way of exploring ordinary themes, and Pratchett is a master of fantasy. Without the Discworld trappings, the plot and characters would be very familiar, and the comedy would still be first-rate.

The comic effects are greatly enhanced, however, by the absurdity of the Discworld, which...