In October of 667 A.D., Fidelma of Cashel - sister to the one of kings of Ireland, a religieuse of the Celtic Church, and an advocate of the Brehon courts - is struggling with her most challenging role yet, that of mother to her infant son Alchu. So it is with mixed feelings that she receives the summons from Abbot Brogan. There have been a series of shocking murders that have terrorized the villagers near the Abbey of Finbarr; three young girls have been violently slaughtered - one per month of the night of the full moon, the most recent only days before during the badger's moon, October's full moon. The villagers are angrily demanding answers from the abbey, who are housing three visitors from faraway—strangers who the villagers believe are behind the gruesome murders. As a respected Brehon, Fidelma, along with her companion Brother Eadulf, is dispatched by her brother the king to restore order to the panicked village and investigate the killings. But time is running out and Fidelma must act quickly, uncovering the complicated truth before the next full moon comes and the lunatic killer strikes again.