"Red Harvest" by Dashiell Hammett.

Almost 100 years old, and it is still one of the best things you'll ever read.

If the plot sounds familiar, it's because it's been stolen over and over and over.

A private detective is hired to investigate corruption in a small city. When the man who hire him is gunned down, the unnamed hero decides to set all the town's gangs at each others' throats to see what shakes out.