Checking into the convent of the Sisters of the Sacred Light does nothing for the explosive sibling rivalry in this sequel to the paperback The Sibling, Trevor's latest break from his Quiller spy novels as Adam Hall. Their school is a shambles; their friends are being cut down by drugs or Russian roulette or psycho episodes that make them take out their guns in class and blaze away; their workaholic parents come home only long enough to fight--so Madlen and Debra Felker decide to take refuge in a rigorous order they hope will provide them with a better, or a least a less toxic, world. Their intake interview, after an evening spent boning up on the Catholic Church, provides a few precious moments of high comedy before the curtain comes down for good. Beyond all the expected privations--no mirrors, no hair, no talking after evening Recreation--there's real trouble brewing: Debra, who was adopted as an infant, suspects that her brushes with death (a fire in an off-limits tunnel, a close encounter with a fatal dose of mushrooms, an exploding oil lamp) aren't just bad luck: her ever-so- solicitous sister is trying to kill her. Though Debra's too paralyzed with terror and depression to do anything about Madlen, Trevor's blessed her with several guardian angels: her heretofore unsuspected Aunt Helen, jailbait Mafia princess Sister Nicola Montoni (on sabbatical after her husband's concrete-overshoes drowning), and Father Giovanni Falconi, the hunky veteran of the Bronx Nicola's set her rapacious sights on. Will these unlikely allies be able to save Debra from her sister--or from her own paranoid fantasies? An expert but synthetic timekiller--minor work from a sometime master.