The Heretic's Apprentice A Medieval Whodunnit

This book examines what true piety is. The main character is the apprentice of a man, now dead, who is suddenly accused of having been a heretic.

In this book, Edith Pargeter (aka Ellis Peters), through her hero Brother Cadfael, examines where heresy overlaps with true inquiry. Her characters are vindicated for pondering the mysteries of Christianity, including the trinity.