A bit of a sophomore slump for Josephine Hart, I think.
I've read and enjoyed all of her other twisted little novels: Damage, The Reconstructionist, Oblivion, The Stillest Day. Sin just isn't quite up to par, somehow. Maybe there's a bit too much going on; I think the other books limit the perversions and passions on which they focus, to greater effect.
It's the story of two sisters, one light, one dark. One good, one bad. The good little blonde girl is actually not a true sister at all. She's a cousin orphaned in infancy, raised by the bad little dark girl's parents as their own.
When the two girls are small, naughty, jealous Ruth filches Elizabeth's trinkets and toys. As they grow up, Ruth covets and seduces Elizabeth's lovers, until she finally sets her sights on Elizabeth's adoring husband. Ruth can't make any inroads, however, and before her campaign can meet with either success or definite failure, Elizabeth's husband dies, leaving her with a young son (the only male in Elizabeth's orbit left for Ruth to cultivate).
Ruth marries as well, and also has a son. And then into the pale, sad sister's mourning comes a new man. His initial interest is in the family publishing business, but soon his attention shifts to Elizabeth, which turns Ruth's attention on him. When the family patriarch dies of a heart attack, Ruth seizes the opportunity to plunge into an affair with the man who only recent became Elizabeth's second husband.
The two embark on a lengthy affair, one the allows Ruth to give full rein to her obsession with Elizabeth as she wears and deploys the items she continues to pilfer and hoard -- a silk slip, a pair of black pumps, etc.
The affair continues, and the families teeter and totter along. Ruth's husband is close to leaving her, but she pulls him back. Her brother-in-law tries to break off the affair, but she plots to draw him in again.
Then tragedy radically alters the landscape. On a weekend visit to the family manor, Elizabeth's son tries to swim in the lake (a bid to impress his Aunt Ruth). He suffers an asthma attack in the water, and Ruth's son plunges in to try to save his cousin. The thrashing panicked Steven clings to his cousin and pulls them both beneath the water. Both boys die.
Ruth's husband decides that any other pain will be dwarfed by the grief they all share, so he announces to Elizabeth that her husband and his wife have been having an affair. Elizabeth rejects her husband, and retreats to live alone in Scotland.
Ruth's husband leaves and her lover returns, but she is not satisfied by what would seem to be her victory at last of the more favored child. She turns more and more to the items of Elizabeth's she has hidden away, wearing her clothes and even buying a blonde wig. Finally, she is compelled to seek Elizabeth out.
Elizabeth is living quietly at her cottage, painting and being romanced by a very young man. Ruth tries to continue her hatred of Elizabeth, but she breaks down in tears, vomit and urine. Elizabeth washes her, puts her to bed, and then dresses her in her own clothes. Ruth wearing Elizabeth's clothes again, this time freely given by Elizabeth. And finally the dark sister seems to relinquish some of the obsessive jealousy and hate that have shaped her entire life.
"And if I'd never met her, would I have been good?" Ruth asks. "Did she create me? Or I her? Did I dream her? Am I Elizabeth? Now?"
But then I was never ambitious. Few people are. Perhaps there is in us some inherited, ancient knowledge. The majority do not desire the world--knowing on some primitive level that it disappoints. They are quite content to let the blind few pursue their path to wisdom. And to watch those trapped by genius forced to sacrifice themselves, and those trapped by talent to emulate them. Much better to be in the audience, watching the actors find the surprise ending.