The Auditors of Reality - cosmic beings who despise the untidiness of life - commission a clock so accurate it will stop time itself. Only the History Monks, who maintain the flow of time across the Disc, can prevent it. Susan and a young monk named Lobsang must find the clockmaker before he finishes his work. Pratchett's most ambitious metaphysical comedy, a novel about time, chocolate, and the things that make life worth the trouble.