A remote island. A group of prisoners. And an evil as old as time. Robin didn't mean to break the law. Didn't know at first what law she'd broken. And now she's on her way to Salt Rock - a new-model prison for a new kind of criminal, way out in the remote Northern Isles of Scotland. On Salt Rock, she'll meet other prisoners like her - men and women from all over the world, spirited away from the lives they knew for crimes they didn't know they were committing. She'll uncover the complex web of conspiracy that connects them all, confronting some of the darkness of her own past in the process. And she'll come face to face, finally, with an evil as old as the land itself. It's hell in those waters.