Dead man's ransom - Ellis Peters

In the February of the year of our Lord 1141, men march home from war to Shrewsbury, but the captured Sheriff Gilbert Prestcote is not among them. Elis, a young Welsh prisoner, is, and he is delivered to the Abbey of Saint Peter and Saint Paul to begin a tale that will test Brother Cadfael's sense of justice . . . and his heart. By good fortune, it seems, the prisoner can be exchanged as Sheriff Prestcote's ransom. What none expects is that good-natured Elis will be struck down by Cupid's arrow. The sherrif's own daughter holds him in thrall, and she too, is blind with passion. Now regaining her father means losing her lover. But then the sheriff, ailing and frail, is brought to the abbey's infirmary and murdered there. Suspicion falls on the prisoner, who only has his Welsh honour to gain Brother Cadfael's help. And Cadfael gives it, not knowing the truth will be a trial for his own soul.