This book is a flashback in Jack Reacher's timeline back to when he was still in the army. The time is set sometime after the fall of the Berlin Wall but before Sept 11.
Reacher gets orders to report to a training class. When he arrives he finds that there are only 2 other pupils - one from the CIA and one from the FBI. He rightly suspects that the purpose of the orders was not training but some secret mission and he was right.
It seems the CIA has information that terrorists were preparing to make a major purchase. The government wants to know what they and purchasing and to stop it. Hence a select group was picked to investigate and take whatever action is necessary.
Reacher's side kick Sgt. Neagley makes a reprise as she assists Reacher in his investigation.
This book is not so much an action story as it is a mystery suspense novel as it follows Reacher and Neagley as they decipher what is being sold and by whom. The plot is tightly woven as it tells pieces of the story from the points of view of the various characters. Highly recommended and a good change of pace for Lee Child.