Ireland, AD 671. An Anglo-Saxon delegation arrives at Cashel to debate religious rules issued from Rome, while Irish church leaders resist what they regard as foreign interference. Eadulf's estranged younger brother Egric is among the visitors, making the increasingly hostile proceedings personally difficult as well as politically dangerous.
When the abbess mediating between the factions is beaten to death, suspicion falls on both sides of the dispute. Fidelma and Eadulf must examine the delegation's private loyalties, the meaning of a disputed seal and the resentments surrounding Egric before the murder turns a theological disagreement into violence between kingdoms.