P. D. James on the Mystery Genre

The mystery’s very much the modern morality play. You have an almost ritual killing, you have a murderer who in some sense represents the forces of evil, you have your detective coming in–very likely to avenge the death–who represents justice, retrib…

The mystery's very much the modern morality play. You have an almost ritual killing, you have a murderer who in some sense represents the forces of evil, you have your detective coming in--very likely to avenge the death--who represents justice, retribution. And in the end you restore order out of disorder.

P. D. James, English mystery novelist 

from http://jimfishertruecrime.blogspot.com/