THINK OF A NUMBER
So John Verdon arrives on the scene with a cliche-ridden brick of a book about a genius detective whose obsessive behaviour is damaging his marriage and so he has retired from the NYPD to upstate NY where everything will be much better...if he doesn't get dragged into solving a mystery for an old college mate who is being sent freaky hand-written messages by a scary person who seems to know more about the recipient than is reasonable for anyone.
It's obvious where this is going to go and it does, but nevermind - Verdon has crafted a page-turner with vivid even if off-the-shelf characters. There's a technique he uses to show off his protagonist's skills. In group interactions he likes to set up a moron (always a bloke) and a sharply perceptive and well educated woman to compare and contrast with his hero. In fact he'll try to squash in several types of moron if he can. No wonder he was the most celebrated detective in NYPD history with all those other idiots about - in fact it's amazing any crimes get solved now he's retired - oh! They don't - he has to come back and do it for them...
There are zillions of other books out there about psychos and genius detectives but most of them are far less worthy of your time than this one.