Jeffrey Clayton, a criminology professor and noted expert on serial killers, is handed an unusual assignment: tracking down a mass murderer who just might be his long-presumed-dead father. Seasoned fans of Katzenbach (The Shadow Man, 1995, etc.) probably won't object to the light psychological treatment given to this almost like-father/like-son story whose setting in the dreary near future adds an original note to the basic formula. Clayton, a withdrawn academic whose fear of his students is justified in an increasingly violent age (everyone, it seems, now packs guns), grudgingly accepts the job of hunting for his father from Martin, an agent employed by the state security arm of the soon-to-be 51st state, a multicorporate holding carved from several western states that promises total safety in exchange for the suspension of certain basic constitutional rights. Martin, it turns out, had questioned Clayton senior some 25 years before about a killing, but because of lamentable constitutional safeguards (the author is forever ambivalent in this regard) he let him go; now a spate of killings marked by the same MO seems to indicate that Jeffrey's father is back in business. Meanwhile, his sister Susan, a crack shot and professional puzzle-writer who lives with the siblings' terminally ill mother, Diana, in the Florida Keys, has suddenly begun receiving cryptic notes; a superb decipherer, she realizes independently that their menacing father still lives--and is out to get them. Susan and Diana, toting a small arsenal, join forces with Jeffrey, and the three cleverly piece together a host of disparate clues that lead them to the final, talky confrontation. Less gory than one might expect, and less psychologically compelling than the narrative would want us to believe: Katzenbach is not likely to keep anyone guessing too long, but the action is fast-paced and most of the story's loose ends are smartly tied.