When Baron Herbert returns from the Crusades despondent instead of rejoicing and his sons begin to die in strange accidents, people wonder whether God is punishing him for some dark sin. The baron pleads with his friend Sir Hugh of Wynethorpe to bring healers to his castle, and Hugh, Brother Thomas, Prioress Eleanor of Tyndal, respected physician Master Gamel, and healer Sister Anne arrive just in time to witness the death of a third son. While many say the deaths are due to the devil or God's wrath, Thomas and Eleanor believe a mortal murderer is to blame.