AD 671. Sister Fidelma has a mission, and she is sworn by oath to reveal her purpose to no other. The secret investigation leads Fidelma and her companions to the abbey of Finnbarr to question the abbot.

But before they have a chance to speak to him, the abbot is found murdered - and the young girl suspected of the crime has fled the scene. Despite their protests, Fidelma's cohorts agree to accompany her in pursuit of the girl for answers. But as vicious rumours spread, accusing Fidelma's family, the Eóghanacht Kings of Cashel, of conspiring to assassinate the High King and abduct his wife, Sister Fidelma's life is placed in mortal danger.

Unable to tell the truth of her quest to anyone, including her husband Eadulf, Fidelma's time is running out - and now she has no choice but to face the challenge, and her enemies, alone.