In the earlier day, Jack Reacher is what he is, hard and tough and want nothing to live one day at a time.
Trouble find him, or there wouldn't be a story.
And in the process, he found a woman he knew when she was still a teenager.
Now she is no longer a teenager, they could be together.
This is more than just the usual fling. This is more than that.
She is in danger of some sort because someone is shooting at her. Jack is going to play body guard and lover.
There are some subplot that seems like a distraction but now going into the main story.
Jack is investigating a disappearance of a solider in Vietnam war. That's a long time ago so why is it still classified? In the meantime, he discovered the parents of the missing soldier were conned.
Further investigation found more details about this missing person.
Pretty good storytelling.