This is the fourth book in Terry Pratchett's books on the Discworld - a flat world, supported on the back of four massive elephants riding on the back of a planet-sized turtle, anything hilarious can happen here, and eventually does. In this book, Death (capital "D", he's the man, or rather the anthropomorphic personification) decides to take an apprentice, and selects Mort, a rather inept young man from the Ramtops. As Death takes less interest in his job, Mort's interests cause him to create a tear in reality.
This is another great Pratchett book. Running several storylines at once, the author succeeds in having all of them move along smoothly. Also, the book contains a goodly dollop of Terry's humor and ironic footnotes. I love the Death books (this one, plus Reaper Man, Soul Music, and Hogfather); in this one Death tries the joys of drinking, dancing, gambling and so forth, all with hilarious results.
I wholeheartedly recommend this book.