Dead Man's Ransom by Ellis Peters

Set in the tumultuous period of the 12th century, this historical mystery unfolds as Brother Cadfael, a former soldier turned monk, finds himself embroiled in the aftermath of a battle between the forces of King Stephen and Empress Maud. When a Welsh prince is taken hostage and a ransom is arranged, the situation becomes complicated by the murder of a young squire. As tensions rise between the English and the Welsh, Cadfael must use his keen intellect and knowledge of human nature to unravel the truth behind the murder, navigate political intrigue, and ensure justice is served, all while maintaining peace between the two factions.