This is the fourth Keller book. Keller is like a lot of us -- he's isolated, usually single, drifting through life. He's also a professional hitman.
This books starts with him buying stamps (he's a collector), hanging out while he's waiting to carry out a hit. But then there's another, highly political hit, and he gets framed for it.
So he flees across country, trying to get back to his apartment in New York. As they've broadcast a picture of him, and track down what his rental car and license plates are, this is a bit difficult. It's made even more difficult because he spent most of his cash on stamps, and doesn't dare use his faked credit cards.
He makes it to New York, realizes there's nothing there for him, and strikes out across country again. He ends up taking a break in New Orleans, in one of my favorite passages from the book:
On the other hand, could he really drive all the way to New Orleans, then turn around and drive out again, only to sustain himself with prefabricated burgers and fries from yet another soul-deadening fast-food joint? That hadn't been so bad in Tie Plant, Mississippi, or White Pine, Tennessee, where one's choices were limited, but Keller had been in New Orleans a few times over the years, and he could still remember the beignets and chicory coffee at Cafe du Monde. And that was just the tip of the Tabasco bottle -- could he really leave this city without a bowl of gumbo, or a plate of red beans and rice, or an oyster po'boy sandwich, or jambalaya, or crawfish etouffee, or any of the spectacular dishes you could get virtually anywhere in New Orleans, and nowhere else in the world?
He has a chance encounter that causes him to go to ground, and he starts building a life again.
Overall, I enjoyed the book. He spends even more time isolated and alone than usual, and it has his normal deadpan reactions and going along with events as they occur.
I think it was basically a retirement novel, giving Keller a graceful and satisfying end to his career, albeit once that Block can always pull him out of if he feels the need.
If you like Keller, you'll probably like this book. If you haven't read any Keller yet, start with Hit Man instead, it's the first one and, I think, the most delightful. On the other hand, these books aren't spoiled by reading them out of order, if you happen to have a copy of any of the four there's no reason not to start with that one.