Yorkshire, 1983. Margaret Thatcher is in Number 10, 'Thriller' is on the radio and Lorraine Quick is having to put plans to tour with her band on hold due to work. With her expertise in psychometric testing, she is being sent to the Yorkshire moors to build a PR-friendly team out of the ragtag staff of the infamous Windwell Asylum as it transitions into a modern, top-security unit housing some of the most dangerous criminals in the country.
And then Lorraine stumbles on a brutal murder that has taken place despite the fifteen-foot-high perimeter wall and the heavy-duty locks. Between the asylum's lingering reputation for violence, the haunting underground tunnels of the old institution and the arrival of almost-old flame DS Diaz to investigate the murder, events are coming to a head for Lorraine.