Cadfael's novice, Brother Oswin, is found close to death, babbling about a woman, out in the woods in mid-winter. Cadfael goes out to try to find out what happened to him and the small traveling party he had met up with, when he finds one of them, a young nun called Sister Hilaria, raped, murdered and encased in the ice of a frozen stream. Suspicion of her murder falls on Oswin, who is no state to convincingly deny it. Cadfael tracks down the two other members of the party, Ermina and Yves Hugonin, and sets out to prove Oswin's innocence.