Thief of time : Discworld ; bk. 26
(Book)

On Discworld, the managent of time is entrusted to the venerable Monks of History, who store it and pump it from where it's wasted, like underwater, to cities, where citizens are forever asking, "Oh where does the time go?" Going against everything known, a young horologist has been commissioned to build the world's first truly accurate clock, but if the Perfect Clock starts ticking, time as we know it will stop. History Monk Lu-Tze and his apprentice Lobsang Ludd must find the timepiece and stop it before it starts.