The cloistered walls of Shrewsbury Abbey have always protected Brother Cadfael from the raging Civil War. But when fighting escalates between Empress Maud and King Stephen, the war takes a deadly step closer to him. Taken prisoner in the battle for Maud's land is Olivier de Bretagne, Brother Cadfael's own son- born as a result of a brief encouter thirty years earlier. Now Brother Cadfael resolves to plead for his son's release at a peace conference scheduled to take place in Coventry; but there is no sign of Olivier there.

After much soul searching, Cadfael makes the difficult decision to break his monastic vows, leaving Coventry without permission- because he knows he must do everything in his power to find his son.