This is book 16 of the "Jack Reacher" series.

This note contains spoilers for the book.

Reacher's terminal assignemnt in the MPs.

We, and apparently the Army, don't know if the up-and-coming Ranger Captain (who is the son of a senator) has murdered a woman, but the Army is going into ass-covering mode (the senator actually sits on the committee that makes or breaks them). It gets worse when Reacher discovers some earlier murders fitting the same pattern.

And even worse when he's presented with evidence that the Sheriff in the country, a retired Marine MP, may be doing it herself.

He's sleeping with her by then. But he's not especially weirded out. And without worrying too much about his judgment being clouded, he concludes the file is a fake. Her rank history is not believable, there are two dead people and a nonexistent person who are important in the story, stuff like that.

So, it's the Captain after all (the first obvious suspect, to me at least). So reacher executes the Captain and the senator, makes it look like an accident to cover the Army's ass, and even dictates a press release blaming the murders on a guy the Tennessee militia killed accidentally while guarding the base at the request of the Senator (not proven).

But the downsizing of the Army is too big, and he's out anyway. So he wanders off in some random direction into the sunset, by bus.