DS Carmichael is accompanying his step-sons on their 'trick or treat' rounds in Castle Farthing, while DI Falconer holds the fort at Market Darley police station this Hallowe'en. In fact, it is DC Roberts who has drawn the evening's short straw and has been dispatched to the small town of Carsfold, to the south of the market town, for a second interview with a householder, without a clue that an unexplained explosion will not only land him in hospital yet again, but kick off another case of murder for his two colleagues.