Showing Dead Man's Ransom by Ellis Peters

The year is 1141 and civil war continues to rage. When the sheriff of Shropshire is taken prisoner, arrangements are made to exchange him for Elis, a young Welshman. But when the sheriff is brought to the abbey, he is murdered. Suspicion falls on Elis, who has fallen in love with the sheriff's daughter. With nothing but his Welsh honor to protect him, Elis appeals to Brother Cadfael for help. And Brother Cadfael gives it, not knowing that the truth will be a trial for his own soul.