Ireland, AD 672.

The abbey of Muman at Imleach Iubhair is being renovated when its guests' hostel burns to the ground. There is one fatality: Bishop Brodulf of Luxovium, a distinguished visitor and cousin to the King of Franks. Sister Fidelma is asked by Abbot Cuán to investigate the unfortunate incident and soon finds that the bishop had been stabbed to death before the fire had even started.

Thrown into a world of treachery and jealousy, where religious beliefs are vehemently disputed, Fidelma and her companions, Eadulf and Enda, face a barrier of deceit. The abbey, a leading ecclesiastical teaching institution as well as a conhospitae, housing both men and women, is divided into factions. Can Abbot Cuán trust Prioress Suanach, who is in charge of the sisterhood? Can the professors trust each other as well as their students? Moreover, can suspicion be levelled at the builders working on the abbey under their dominant Master Builder, Sítae? As more deaths follow, Fidelma must use her wit and ingenuity to unravel the complexities of this intricate mystery.