Some murder cases you can't forget. No matter how hard you try.

For Auckland Detective Matt Buchanan it's Samantha Coates: the innocent girl who disappeared on her way home from school twelve years ago.

All the police found were her clothes discarded on a pristine stretch of New Zealand coastline, and the investigation quickly went cold.

But when the body of another young woman turns up on the same beach many years later, it's all Buchanan needs to reopen both the case and his biggest obsession.

As he pieces the terrible crimes together it becomes clear that Samantha Coates is the only mistake the killers made. And Buchanan must follow the sound of her voice to make them pay for it.