It is four years since the death of King Edward I, but his reign of terror has cast long shadows over the kingdom. At Holyrood Abbey, sheltered in the depths of the Welsh march, the old king's former bodyguards protect his secret relics and watch over a mysterious prisoner who is kept in the abbey's dungeon.

But their peaceful existence is shattered when Abbot Henry is poisoned. Summoned to Holyrood, Sir Hugh Corbett, Keeper of the Secret Seal, finds the fortress in chaos. Brothers Anselm and Richard have been brutally slain by nails driven deep into their skulls.

No one knows who could be behind the gruesome killings and the news attracts the attention of two unwanted guests: the sinister Marcher Lord Mortimer and King Philip of France's devious envoy De Craon. As more mysterious deaths occur, and a violent snow storm sweeps through the valley, Corbett must act quickly to identify the malevolent demon who has risen from hell to turn the abbey into a house of murder...