Prior Herluin and his apprentice, Tutilo, arrive from a distant abbey that has been sacked in the civil war, requesting the loan of the bones of St Winifred. Abbot Radulfus finds it hard to refuse him, but then a local benefactor comes to his rescue, and he decides to keep the holy casket. Then a beautiful slave girl, Daalny, and the bones of St Winifred are abducted from the Abbey, and Cadfael is commissioned by the abbot to find them both. But a man is found murdered before Cadfael can determine what has been happening.

When the corpse of an old man is discovered in a sack at the Abbey, Cadfael believes the man has been murdered. Among the suspects are a group of pilgrims, including two thieves. Cadfael imprisons them in a bid to draw out the killer.