Detective Sergeant Frank Heriot is healthy, happily married, and has a good job. So what has made him cold and remote towards his family? And why is he suddenly plagued by terrible headaches? Is he mentally ill or is something far more sinister affecting his mind? Gradually, the answer becomes clear: Frank is the victim of an unknown force seeking to undermine public confidence in the people and institutions that form the backbone of the British Establishment. Doctors, teachers, scientists, clergymen and writers and are all among its targets; its ultimate aim is anarchy. Where will the mysterious menace strike next? It could be the man who sits next to you on the bus. It could be you...