A French nobleman deserts his wife because of an ancient family secret.

When Philippe de Montfaucon (the Marquis de Bellac) is informed that for the 3d successive year his vineyards near Bordeaux have failed to produce, he instructs his wife, Catherine, to remain in Paris and then leaves for his ancestral chateau. But Catherine, disturbed by his behavior, follows a few days later with their two children. Upon arriving at the chateau, she is greeted coldly by Countess Estelle, Philippe's aunt, diffidently by Père Dominic, the local priest, and disdainfully by the menacing Christian de Caray and his equally hostile sister, Odile. Informed that her husband has gone to a nearby town for the day, Catherine wanders into a chamber in the chateau and accidentally spies Philippe and 12 other men engaged in a mystic ceremonial rite. She is soon afterward terrorized in the Bellac woods by 12 hooded men, and later she learns that Philippe's father, believed dead, is actually living in a turret of the chateau. From him she hears of the dreadful fate her husband has set for himself: tradition decrees that whenever the vines fail for 3 years the head of the Montfaucon family must offer his life's blood as a sacrifice to the barren earth. Horrified, Catherine races from the chateau to summon help. But she is stopped by Père Dominic and taken back to Bellac, while Philippe and the 12 hooded horsemen ride through the village. She escapes but is too late to prevent the death ritual as Christian shoots an arrow into her husband's heart. The next day Catherine leaves with her children, vowing never to return. But she is unaware of the significant glances exchanged between Père Dominic and her young son, Jacques. The new Marquis de Bellac already knows that the ancient tradition must be carried on.