Preparations for the religious celebrations for the Emperor's birthday are brought to an abrupt halt when the murdered body of a visiting ambassador from Rome is discovered in the temple of the Imperial cult and once again Libertus is called upon to investigate. Events take a bizarre turn when the body disappears, and then unearthly wails are heard coming from the temple and mysterious bloodstains start to appear from nowhere. A mood of superstitious terror grips the townspeople and Libertus soon finds himself in grave danger when he becomes the target of an angry mob, accusing him of incurring the anger of the gods and demanding his death to appease them. But could there be a more human explanation for the murder? Perhaps the answer lies with the old High Priest of Jupiter, who is still nursing political ambition, or Scribonius, the assistant Imperial priest whose pious facade conceals a dark secret from his past. Or what about the miserly Optimus, the retired legionary officer, rumoured to be interested in the High Priest's unhappy young wife? Nothing is as it seems, and Libertus is to uncover still more unsettling events, and more deaths, before the truth is finally revealed.