Guards! (Discworld), Terry Pratchett

The eighth Discworld novel

An aura of mean-minded resentfulness is thick in the streets of Ankh-Morpork. Insurrection is in the air. The Haves and Have-Nots are about to fall out all over again. The Have-Nots ant some of their own magic. But magic in the hands of amateurs is a dangerous thing.
 
The City Watch is the last line of defence against such unnatural goings-on. But when even the Watch have trouble telling Right from Wrong, you know that Law and Order ain't what it used to be. But that's all about to change.