Terry Pratchett has a seemingly endless capacity for generating inventively comic novels about the Discworld and its inhabitants, but there is in the hearts of most of his admirers a particular place for those novels that feature the hard-bitten captain of the Ankh-Morpork City Watch, Samuel Vimes. Sent as ambassador to the Northern principality of Uberwald where they mine gold, iron, and fat--but never silver--he is caught up in an uneasy truce between dwarfs, werewolves, and vampires in the theft of the Scone of Stone (a particularly important piece of dwarf bread) and in the old werewolf custom of giving humans a short start in the hunt and then cheating. Pratchett is always at his best when the comedy is combined with a real sense of jeopardy that even favorite characters might be hurt if there was a good joke in it. As always, the most unlikely things crop up as the subjects of gags--Chekhov, grand opera, the Caine Mutiny--and as always there are remorselessly funny gags about the inevitability of story: They say that the fifth elephant came screaming and trumpeting through the atmosphere of the young world all those years ago and landed hard enough to split continents and raise mountains. No one actually saw it land, which raised the interesting philosophical question: when millions of tons of angry elephant come spinning through the sky, and there is no one to hear it, does it--philosophically speaking--make a noise? As for the dwarfs, whose