Alison Willetts is unlucky to be alive. She has survived a stroke, deliberately induced by a skilful manipulation of pressure points on the head and neck. She can see,hear and feel; she is aware of everything going on around her, but she is completely unable to move or communicate. It's called Locked-In Syndrome. In leaving Alison Willetts alive, the police believe the killer's made his first mistake.

Then D.l.Tom Thorne discovers the horrifyingtruth;it isn't Alison who is the mistake, it's the three women already dead. 'An appropriate margin of error' is how their killer dismisses them, and Thorne knows they are unlikely to be the last. He must find a man whose agenda is terrifyingly unique, and Alison, the one person who holds the key to the killer's identity, is unable to tell anyone ...