In the 14th century, thousands of volunteers in matching white robes marched through plague-stricken towns whipping themselves until they bled, believing their pain could save the world. This episode explores the flagellant movement as a profound study in the mechanics of fear, faith, and the human need for control when everything else has failed.

We trace the practice from monastic mortification of the flesh and figures who codified exact lash counts, through the 1260 public processions sparked by a hermit's vision, to the mass continent-wide movements unleashed by the Black Death. We examine the strict, almost bureaucratic rules of the Brothers of the Cross and the tragic paradox that their roving campaigns helped spread the very disease they hoped to stop.

• The spiritual economy that treated sin as a quantifiable debt paid in p ...