Zane is a failing photographer in a world in which science and magic both work. On a very, very bad day, he wanders into a magic shop and makes a deal with the proprietor which winds up making his day even worse, and decides to kill himself.
In the apartment from which he is about to be evicted, he prepares to shoot himself, and is in the act of pulling the trigger when he is interrupted by Death.
The actual personification of Death.
Startled by the interruption, he moves while his finger is still pulling on the trigger, and accidentally kills death, instead.
He doesn't understand that this is Death whom he has just killed, and he is completely unprepared for the arrival of a middle-aged woman who introduces herself as Lachesis and tells him that, having killed Death, he is now the new Death. His troubles, of course, have only begun.
It's an interesting set-up. The five Incarnations--Death, Time, Fate, Nature, and War--are all offices filled by previously-mortal human individuals who serve until they resign or, in the case of Death, are killed by their successor. New occupants of the offices need to learn their roles, and in Death's case, well, Zane is going to have to learn quickly. As he learns the basic aspects of his new role, he discovers that his new colleagues have set him up to play a key role in a conflict with Satan.
This is a fun romp, not nearly as deep as Anthony would like to think it is (there's an afterword included), but it doesn't need to be. It can be enjoyed as just plain fun, especially if you refrain from pursuing awkward questions about plot holes and "how could they possibly not have noticed..."
I bought this book.