Tripwire — Lee Child

Ex-military policeman Jack Reacher is in Key West enjoying a sort of lazy anonymity when a stranger shows up looking for him. The man has a lot of questions--too many. Hours later, he's dead. And Reacher is forced to follow the man's cold trail back to New York to find the people who dispatched him in the first place: an alluring and intelligent woman from Reacher's own haunted past; a bewildered, elderly couple still mourning an all-American son lost in Vietnam; and at the center of the web, an opponent, more vicious than any he's ever faced...