Z is for Zachariah, the last name in fifteen-year-old Ann Burden's Bible school alphabet book; it's also for zero population after nuclear bombs and nerve gas seem to have destroyed everyone in the world except Ann in her Amish country valley (her family left it and seem singularly unregretted but then Ann is one of those unthinking practical types) who is making it alone with her brother's dog Faro, with their cow, chickens, the diminishing supplies from the store and her garden. Until a stranger comes over the hill in his plastic safe-suit -- he'd killed to get it; he has a bout of radiation sickness and almost dies but Ann brings him back to health only to face a lethal gratitude on his part. Mr. O'Brien wrote two juveniles as well as another genocidal thriller, A Report from Group 17. This is a little of each for both audiences and you'll find Ann's level resourcefulness as insulating as that safe-suit. So, less convincingly so, is her abz naivete in a day and age which has just come to an end.