Reaper Man by Terry Pratchett

Death confronts his own mortality in this installment of the Discworld series. When the powers that be decide that Death has too much of a personality and must be replaced, Death learns what it's like to be human (temporarily at least), and, in his absence, the wizards of Ankh-Morpork, faced with an over-load of spirits separated from their bodies, deal with the challenges of a high un-dead population--including the threat of a parasite that preys on cities: the shopping mall! In a book both hilarious and touching, Pratchett succeeds again.