The Auditors are beings who watch the Discworld from above to ensure everything obeys The Rules. As Death starts developing more of a personality the Auditors feel that he does not perform the Duty (namely, sending dead people to the beyond) in the right way anymore.  They send him off with his own golden hourglass and his scythe to live like everyone else. Now called "Bill Door", he tries to work as a helper on a farm. Meanwhile, the rest of the Discworld has problems of its own. While every other species thinks of a new Death for themselves in seconds, humans "are capable of believing in very complicated things", and need a bit more time for their Death to be completed. As a result, the "life force" of dead humans starts to build up; this results in poltergeist activity, ghosts, and other paranormal phenomenon. Most notable is the return as a zombie of recently deceased wizard Windle Poons, who was really looking forward to reincarnation, and instead finds himself attending meetings of the "Fresh Start Club", an undead-rights group lead by Reg Shoe. Not only that, Windle and his new friends and the wizards of the unseen university discovers the city of Ankh-Morpork is being invaded by a parasitic lifeform that feeds on cities, and hatches from eggs that resemble snow globes.  When humankind finally thinks of a New Death, one with a crown and without any humanity, Bill Door returns to fight him and take back his place.

or Mort Again. Terry effortlessly rewrites the basic premise of Mort, that of Death going on holiday and being replaced, although this time its by a new Death and not a spotty teenager. However to pad the book out and give it some room there's a whole other story added free of charge with only minimal connections to Death's dilemma. The Wizards easily upstage Death imho, they're just so relentlessly stupid and yet comically hysterical. The Burser's slide into dried frog pilldom is well on its way now while Ridcully further solidifies his place as the most gung-ho arch chancellor seen so far, although the Dean does manage to go one further. The Fresh Start club is another good idea, the undead often do get a rough ride of it in fantasy novels, but Reg Shoe is on hand now to put the world to rights.  Death finally does manage to get his old job back, by whacking the new Death, thus proving that he's the better Death for the job, although the Death of Rats will give him a run for his money in future novels...