Brother Cadfael's penance - Ellis Peters

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.