Here's what Anthony Boucher said: "A considerable novel in the best Hammett tradition . . . uncompromisingly hard, admirably told." I couldn't have put it better myself.
I'll add, however, that the book is obviously Westlake's riff on Red Harvest. It's about a private-eye named Tim Smith ("I many be chunky, but I can move fast when I have to." Sound like any p.i. you might have read about?). Smith lives in a small town in New York where he's decided that the best thing for him to do is to go along to get along. He has the dirt on everyone, and it's all in his files, but he's not turning anybody in. He likes the town just the way it is. If there's corruption, that's fine with him, as long as things run smoothly and well.
Then a reform group targets his town, and Smith becomes the target of a killer. What will he do about that, and whose side will he take now? I'm not going to spoil things for you, but I will say that this is a fine example of a novel that's both hardboiled and noir. I first read it more than 40 years ago, and I still remembered the ending.