In April of 1545 a horrific massacre of more than 3,000 heretics in southern France occurred. In one small village, twenty-five women and children hid in a secret grotto in the hills above town. But they were betrayed. Royal and papal troops built a fire in the mouth of the grotto and murdered them all by suffocation. So much is an established historical fact.

Two American couples living in the present village of Barigoule and enjoying the peace and pleasures of Provence discover the history of the local atrocity. They resolve to unearth the secrets still hidden in the deadly grotto, now forgotten after four and a half centuries. But they are frustrated at every turn by the stubborn silence of the locals. Worse, the few who offer to help are murdered.

Finally, they are aided by a French police inspector and his partner, a lovely Muslim woman (and a deadly shot). When an ancient document is discovered that exposes the fantastic outcome of the killings at the grotto, all concerned are forced to flee for their lives until they take refuge in the cave itself, where the savage conclusion to their quest takes place.