After taking a serious beating whilst engaged in unofficial undercover work in the murky streets and taverns of London's 19th century slums, Constable Tom Churchyard takes himself to Cornwall. Here, in spite of his injuries he becomes right-hand man to Amos Hawke, now a senior Cornish policeman. His knowledge of the London rogues proves invaluable as Amos seeks to foil a gang of city thieves whose plan is to plunder the mansions of the Cornish gentry. When a brutal murder is committed during their investigations it proves far more complex than appears at first glance.