Ireland, AD 672. The body of Brehon Brocc is found on a mountain road after he set out on a secret mission with Princess Gelgéis and her steward. When Gelgéis fails to arrive at Cashel for her marriage to King Colgú, Fidelma, Eadulf and Enda enter the hostile kingdom of Laigin to find her.
Local stories blame demonic shapeshifters and brigands working ancient mines, while rumours suggest that Laigin and Muman are preparing for war. As additional deaths follow, Fidelma must determine whether supernatural fear is concealing organised theft, political abduction or a plot designed to destroy the proposed royal alliance.