Andrea Oliver's mother, Laura, is the perfect small-town mum. Laura lives a quiet but happy life in sleepy beachside Belle Isle. She's a pillar of the community: a speech therapist, business owner and everybody's friend. And she's never kept a secret from anyone. Or so Andrea thinks.

When Andrea is caught in a random violent attack at a shopping mall, Laura intervenes and acts in a way that is unrecognisable to her daughter. It's like Laura is a completely different person - and that's because she was. Thirty years ago. Before Andrea. Before Belle Isle.

Laura is hailed as a hero for her actions at the mall but 24 hours later she is in hospital, shot by an intruder, who's spent decades trying to track her down.

What is Andrea's mother trying to hide? As elements of the past return and put them both in danger, Andrea is left to piece together Laura's former identity and discover the truth - for better or worse - about her mother. Is the gentle, loving woman who raised her also a violent killer?