Alison Willetts is unlucky to be alive. She has survived a deliberately induced stroke, and although she can see, hear, and feel, she is completely unable to move or to communicate. In leaving Alison alive, the police believe her assailant has made his first mistake. Until Detective Inspector Tom Thorne discovers the horrifying truth: Alison is the psychopath's first success the three women he killed before her were the mistakes. "An appropriate margin of error" is how their killer dismissed them: his true intention was to leave them just like Alison: put to sleep for the rest of their natural lives. And Thorne knows they won't be his last victims. To save innocent lives, he must find a criminal whose agenda is terrifyingly unique. But this untraceable, sadistic madman is smart, elusive, and cryptic - he enjoys toying with the police almost as much as he savors pursuing his sick fantasy - and the only lead Thorne has is the tragically uncommunicative Alison.