Eunice Parchman killed the Coverdale family because she could not read or write." That is the first line and the boiling center of this thoroughly frightening domestic nightmare, an English In Cold Blood that relentlessly--occasionally a bit overmelodramatically--counts the days until stony-faced housekeeper Eunice and her friend Joan Smith, religious fanatic and reformed prostitute, murder the upper-middle-class Coverdales, a Mozart-listening family of kindly "interferers." Every turn of the plot, including the capture of the almost-undetected murderess, is linked to Eunice's secret illiteracy--her constant fear of discovery, her morbid fear of books ("small flattish boxes, packed with mystery and threat"), her exaggerated suspicions of her employers, her surrender to the narcotic of television. Rendell may seem to oversimplify Eunice's warped psyche ("Illiteracy had dried up her sympathy and atrophied her imagination"), but rarely has a fictional crime of madness been designed to snowball with such haphazard inevitability and terrifying ordinariness. The reigning chronicler of crime-from-the-criminal-point-of-view has struck again, with somewhat less elegance than usual but with more sheer clout: weak of heart, beware.