I have to admit this one crossed me up a little. For whatever reason, I was expecting a sequel to 61 Hours, which ended with a huge bang but left a number of loose ends available if required. Instead, we find ourselves willy nilly in darkest Nebraska, one county of which is living under the thumb of the evil Duncan family. We don't know what the Duncans are up to until almost the end; what we do know is that they are determined to track Reacher down before he finds out.
That's one piece of the puzzle. The second is the mystery of what happened to a little girl who disappeared 25 years before. Disappeared, as in never found.
Reacher is big and he's tough, but he's also smart, and he has a code that he lives by. You take a character like that and put him in a story that barrels along, propelled by writing that doesn't try to do too much but knows how to vary the pace just enough: this is a recipe for a winner. The Reacher books are what they are: not great literature, but solid, always readable adventure mysteries.