There's just enough darkening Victorian gloom in this diverting first novel to set the incestuous relationship of a brother and sister in a relatively kindly if decidedly mauve twilight. The deceased father of twelve-year-old Christopher and ten-year-old Cathy has left as a legacy a box of s/m pornographic photographs which prompt the children to fascinated experimentation. Oppressed by the amorous alliances of their lovely, agreeable mother and the sour threatening presence of older brother Edward, the two soul-and-bed mates weather childhood years marked by Cathy's near-fatal illness, peculiar attentions paid Cathy by Mother's French lover, and their growing awareness of an outside world where both will be inadequate. During a seaside vacation, when the siblings are confronted by the sexual advances of others, Christopher decides that they must end what has turned out to be ""wrong,"" even though Cathy insists that they've merely been ""unseen and unseeing creatures, moving side by side toward the same spot in the sunlight."" The anguish of separation and unfulfilled reunions follows--until at last Christopher is doomed to die in South Africa, and Cathy, learning the vicious extent of woman's subjugation (her brother Edward's tortured wife dies after self-mutilation), unwillingly bears a child to her kind but conventionally restrictive husband. These rose confessionals and brown studies are sustained throughout by an easy period decorum and sentiment, and they linger not unpleasantly on the diffused eroticism of childhood and the anatomy of loneliness in a world of sexual hostilities.