In the story, Annie O'Sullivan is a real estate agent who is kidnapped and held hostage for a year by a psychopath who seems to want to bring up a nuclear family away from the impact of the world.
The story isn't told "as it happen." It's told as a series of sessions with a psychotherapist, in which she recounts what she's been going through. This was a clever plot device, but made the book more depressing for the reader, because it made it clear what it was like for her after she returned to "normal society."
In short it's a rattling read. I found it depressing, but you'll want to know what happened to her in the end.
p.s. If you're English, this book will almost automatically remind you of Suzy Lamplugh. The story's bound to be different, but the context is the same.