Wighard, archbishop designate of Canterbury, has been discovered garrotted in his chambers in the Lateran Palace in Rome in the autumn of AD 664. The solution to this terrible crime appears simple as the palace guards have arrested Brother Ronan Ragallach, as he fled from Wighard's chamber.

Although the Irish monk denies responsibility, Bishop Gelasius is convinced the crime is political and that Wighard was slain in pique at the triumph of the pro-Roman Anglo-Saxon clergy in their debate with the pro-Columba Irish clergy at Whitby. There is also a matter of missing treasure: the goodwill gifts Wighad had brought with him to Rome and the priceless chalices sent for the Holy Father Vitalian's blessings have all been stolen. Bishop Gelasius realises that Wighard's murder could lead to war between the Saxon and Irish kingdoms if Ronan is accused without independent evidence.

So he invites Sister Fidelma of Kildare and Brother Eadulf to investigate. But more deaths must follow before Fidelma is finally able to put together the strange jigsaw in this tale of evil and vengeance.