Set in a blazing hot summer in Cornwall the claustrophobia engendered by the heat is offset by the chill that comes from Isabel, who seems to be a selfish and uncaring person much like the mother she grew up with. With the strange, smothering bond that you often find with literary sisters (I'm thinking The Distance Between Us and Dancing at Lughnasa) also prevalent in this tale, it seems hard to know whose side to be on as the story unfolds and nobody is presented in a very flattering light.
Things spiral out of control as Isabel's mental health deteriorates and the presence of her baby son brings to light memories that both her and Nina have suppressed since childhood. In an interview I read with Helen Dunmore about this book, she talks about not giving psychological explanations for her characters' behaviour but letting the readers make up their own minds about things. That's one of the things I like most about her writing, that and the beauty of her prose, and for me the thing that really stands out about Isabel is the conflict she created in me. Sometimes I can justify what she does, sometimes I can't. Sometimes I pity her, other times I think she's a monster. All I can really say is read it and make up your own mind about her, if you can.