The first volume in a projected series featuring Sister Fidelma, a seventh-century nun who is also a d†laigh (or advocate) authorized to practice law in the courts of her native Ireland. The story's set in a climate of religious conflict, brought to a boil when a powerful Northumbrian ruler brings together leaders from the Celtic church and from Rome to determine whose doctrine and practice will hold sway in his kingdom. The murder of an eminent principal in the subsequent debate casts suspicion on both parties and tests the deductive mettle of Fidelma, and of Brother Eadwulf, the handsome young ``Romanist'' monk who teams up with her to investigate--and, we suspect, to forge a relationship that will be further explored in later volumes. The mystery per se isn't much (the killer's identity is easily guessable early on); the dialogue is straight out of 1950s Hollywood historical ``epics''; and Tremayne indulges an annoying habit of conveying bucketsful of period information in every casual conversation. On the other hand, he does keep introducing intriguing new characters virtually throughout the novel. And in the simultaneously sharp-tongued and full womanly figure of Sister Fidelma he's created a heroine whom many readers will willingly follow. Even Brother Cadfael might have tolerated her.