Lapsed Catholic DI Joe Rafferty isn't best pleased when he learns their latest case is at the local Roman Catholic Convent, where a body was discovered in a shallow grave in the grounds. The nuns' order is a closed, contemplative one, and access to their house and grounds, with its surrounding eight-foot-high walls, far from easy.Rafferty is inclined to think this was an inside job. Prejudiced by his rigid schooling, he doesn't find it as hard as his DS, Dafyd Llewellyn, to believe that nuns were capable of murder. But then, events meant that the suspects stretched to include the nuns' doctor and the priest - who turned out to be none other than Father Roberto Kelly, 'the greatest sinner in the parish'.It is, for Rafferty, a difficult case from the start, not helped by the fact that he receives a blackmail letter that very morning. Convinced that one of the nuns had killed the man, Rafferty's question, 'why', requires him to dig deep into the past and to the mores of an earlier generation.