The Amazon Charts bestselling series continues as air marshal Seth Walker hunts a potential terrorist who could hold the key to the darkest chapter of his own past.

When an electrical engineer from one of America's premier tech companies disappears inside the San Francisco International Airport before an overseas flight, air marshal Seth Walker is called in to investigate. With the clock ticking down and questions multiplying at every turn, Walker can't afford to fail: the lives of all two hundred thousand passengers inside SFO may hang in the balance.

As he races through crowded concourses, desperately searching for clues, Walker can sense this is no routine missing-persons case. But as he digs ever deeper into the young man's background, the tangle of contradictions he finds is confounding. Is the engineer the victim of a crime...or the perpetrator of one?

As the case forces Walker to confront his own demons and the reason he fled his former life in industry, finding this man may mean exposing his own darkest secret.