A town gripped by fear.

It begins with contaminated yogurt in a supermarket. Next, the tampering of showers in a girls' locker room. Caustic soda in baby powder. Cholera in cough medicine. An anonymous note promises much more - unless the town of Casltemere pays a ransom of one million pounds.

Superintendent Frank Shapiro, recovering from a bullet wound, has been cleared for desk duty. But with Sergeant Cal Donovan on holiday cruising the Castlemere Canal, he must rely on Inspector Liz Graham as hysteria rises and the fine line between savagery and civility grows narrower by the day.

The situation worsens when the detectives learn Donovan's abandoned boat has been found near the tiny village of East Beckham - and that the volatile sergeant is believed dead by the hand of the blackmailer. Yet stranger twists are still to come, for guilt and innocence wear ever-changing faces, as does evil.