Siren Call

Who is the mysterious woman on the beach who, initially, only Eleanor can see? What do the words 'Give him to me' mean and why does she repeat them?
And then, Bill is left alone at the cottage and the woman appears to him, in a very different form. Can Eleanor piece together the mystery surrounding this spectre before it is too late?
The couple find themselves hurled headlong into a drama which takes over their lives as this ghost-like woman takes over their lives. Is there any amount of humanity left in her cold, heartless body? And can Eleanor appeal to that part of her before she totally destroys her entire family?