Not quite novel or novella, McEwan`s masterful 13th work of fiction most resembles a five-part classical drama rendered in prose. It opens on the anxious Dorset Coast wedding suite dinner of Edward Mayhew and the former Florence Ponting, married in the summer of 1963 at 23 and 22 respectively; the looming dramatic crisis is the marriage`s impending consummation, or lack of it. Edward is a rough-hewn but sweet student of history, son of an Oxfordshire primary school headmaster and a mother who was brain damaged in an accident when Edward was five. Florence, daughter of a businessman and (a rarity then) a female Oxford philosophy professor, is intense but warm and has founded a string quartet. Their fears about sex and their inability to discuss them form the story`s center. At the book`s midpoint, McEwan (Atonement, etc.) goes into forensic detail about their naive and disastrous efforts on the marriage bed, and the final chapter presents the couple`s explosive postcoital