London is under siege. A financial scandal has promoted violent protests. As the anger in the streets detonates, a young homeless man burns to death after being caught in the crossfire between rioters and the police. But things are not quite as they seem. An opportunistic killer appears to be using the chaos to exact revenge, and yet the intended victims seem to be selected in such a mysterious manner that the Peculiar Crimes Unit is called in to find a way of stopping him. Arthur Bryant and John May must hunt down a murderer who is adopting some decidedly incendiary methods of execution.