Terry Pratchett's Thief of Time, confronts Discworld and a variety of its defenders with an insidious menace; never before has the phrase "The End of History" had quite so sinister a sound. In the great stinking metropolis of Ankh Morpork, an obsessed clockmaker receives an unusual commission from an excessively beautiful woman whose feet do not touch the ground; strict school-teacher Susan finds herself summoned by her grandfather Death, to do him a favour; the monks who manage the even distribution of Time find themselves with a recalcitrant novice; and dairyman Ronnie Soak muses on his glory days, when he was the Fifth Rider of the Apocalypse, the one who left before they got famous. As always, the sometimes startlingly surrealistically original, sometimes comfortingly groanworthy, jokes are underlain by some intensely complex ideas and tight plotting. Susan sto Helit makes a reappearance as one of Pratchett's more interesting heroines; the sinister Lady LeJean is one of Pratchett's most interesting villains, particularly once we learn the answer to the mystery about her. There is an attractive darkness to much of the humour here--Pratchett is often at his best when at his darkest.--Roz Kaveney