In this 7th outing, the town of Castlemere is being attacked, but no one knows why. Threats are being made that the perp will do great harm to the populace and Liz Grahame, the DI, must find out who it is before he/she makes good on the threats. In the meantime, Donovan is off recuperating from wounds suffered in the previous outing.
This is one of the best British procedurals around. It is best to start with the first entry so you can see the characters develop over the years. Bannister is an excellent writer, the plots are complex without being obtuse, and Bannister has the reader present as each new piece of evidence is put into mix.
If the series has a flaw, it is the subplots featuring Donovan that the author has begun putting into each book. While the circumstances change, the result is the same - Donovan is the unwitting hero.