As one of the characters in this book says, Sister Fidelma will always be thought of as a religious even though she has left the convent to take her place as a Princess of Cashel. One thing that Fidelma has not left behind is her sense of righteousness and her firm belief in the supremacy of the law. That belief allows her to enter into situations that would confound lesser mortals if not frighten them off altogether. This story begins with an attempted assassination of Fidelma's brother, King Colgu. The assassin is killed, crying "Remember Liamuin" as he plunges his knife severely wounding the king. The man is dressed as a monk who claimed to have an important message for the king from a local abbot. Since no one knows anything about Liamuin and it appears that the monk was not really a monk, Fidelma and her husband Brother Eadulf decide to investigate. Eadulf is hesitant because the investigation will take them into the territory of the Ui Fidgente, a rival clan with whom there exists an uneasy peace.
Fidelma, Eadulf, and Gorman, a warrior of the King's Bodyguard, soon discover that the monk was in disguise when they find his horse and clothing in a woodsman's shelter nearby. They also discover a young girl who knows nothing about the attack on the king and claims to have escaped from servanthood with a local chieftain. She is brought back to Cashel until her story can be unraveled. Fidelma and company then head off to the abbey from where the "monk" claimed to be. After stopping for the night, they are robbed of their weapons and valuables by a group of brigands. They manage to recover their horses and arrive at the abbey with no way of proving their identity which leads to a very cold reception until a visiting monk from another abbey vouches for them. The mystery deepens when they discover that the "monk" was using the identity of a monk of the abbey who was killed in the rebellion against Cashel. His father, who had also become a monk, dies that very evening before Fidelma could finish questioning him. As they continue their travels, they discover more answers which leads to more questions. Eventually, Fidelma will put it all together but not without a certain amount of peril for her and her companions. It seems to me that this story has more than a usual complement of twists and turns.
Peter Tremayne, the alter-ego of Peter Berresford Ellis, is essentially a teacher and he cannot resist adding a bit of education to his stories. In Sister Fidelma, he has created the perfect character to teach about ancient Ireland and early Celtic culture. He writes of a time when Ireland was new to the Catholic Faith, a faith that was distinctively different from that of Rome. Those changes would come in time, but I think Fidelma would lament the loss of the ancestral customs. We tend to think that everything has always been the way we experience it now. Peter Tremayne helps us to see that there are other ways that once worked, and perhaps could work again.