Arthur and Malgwyn are called to the abbey of Glastonbury to settle a matter of great political importance—tin is being mined for export to the Empire. While there, Malgwyn and Arthur meet St. Patrick, a legend in the Church who is there on a mission of his own, to root out the heresy of Pelagius. When an aged monk is found cruelly murdered in his cell, Malgwyn is set with a problem that will test his skills as an investigator. His search for the truth may uncover a conspiracy that could endanger the kingdom.