The Yellow Cross is a harrowing tale of a desperate people in a small corner of France who defied the kings of Europe and the Pope. The Cathars, whose religion was based on the Gospels but contradicted the tenets set forth by Rome, found themselves the focus of ruthless repression. In systematic waves of brutal persecution, thousands of Cathars were captured, summarily tried, and burned at the stake as heretics. Yet so ardent was their faith that...