The American Ambassador by Ward Just (Houghton Mifflin: $17.95; 320 pp.)

“Alienation: a withdrawing or separation of a person or his affections from an object or position of former attachment.” Any parent who has experienced it--seen a son or daughter turn, blankly, away--knows the wrenching sense of desolation and the guilt, or the puzzlement, of the “whys” that swirl around it. What should I, what could I, have done to avoid this? More frustrating than that: Would anything I could have done made a difference, anyway? And in “The American Ambassador,” novelist and former foreign correspondent Ward Just takes a chilling, in-depth look at an alienation that goes far beyond the mere “withdrawing” of “affections.” This is not a study of a son who simply moves across the country, and ignores “duty” phone calls.

Put yourself in the place of a foreign service officer--dedicated, seasoned and proud of his distinguished career representing the United States in half a dozen countries.

Then watch as the evidence becomes incontrovertible that the son that he and his loving and talented wife have reared is now a key member of a murderous German-based terrorist group--a random assassin and a bomber of the innocent. For William and Elinor North to ask: “Where did we, or he, go wrong?” is as futile as asking “why did this cell turn cancerous while this one did not?” At the very least, “The American Ambassador” is a gripping international thriller as North and the colleagues who share the knowledge of his son’s involvement try to unravel the motives, and the targets, of Bill Jr.’s German group.

This is both the anatomy of a terrible personal tragedy that shakes some of the elder North’s long-held ideologies, but it is equally an inner struggle between his conflicting loyalties--to the son he still loves, but also to the country that he equally loves, and as his son bitterly reminds him, to whom “you took an oath to defend . . . against people like me. Enemies foreign and domestic. Enemies without and within. I’m both. What happened to your oath?”

Just, in this, his 10th novel, raises the hackles on the back of his reader’s neck as, slowly, it becomes all too clear what Bill Jr.’s next lethal target really is: Bill Sr.

What turns a bright, if introspective, child into an irrational animal--one who sees the world spinning out of control and whose only goal in life is to hasten the spinning until, as one character says in analyzing the terrorist mind, “the whole thing, like the tigers in ‘Little Black Sambo,’ turn to butter?” Just shapes and lays bare his characters--and the inner turmoils that drive them--with a deft hand. If the why of Bill Jr.’s soul-consuming conversion to terrorism is never laid out neatly for the reader--like a tray of hors d’oeuvres--but remains largely a riddle wrapped in an enigma--then isn’t that as much of the fabric of terror as the terrorists themselves?

This is a scary novel for anyone who has seen a certain look flash over the face of a child he loves. A common, and passing, expression of filial exasperation, or the beginning of something much, much darker?