Year 1607. In his study, Achille Gagliardi, a priest now dying, tells his seminarian about the events that took place more than twenty years earlier, when the Cardinal Archbishop of Milan went on a pastoral visit to the Swiss valleys.

Year 1583. Leonardo is a young priest-in-training who is sent undercover by Achille to work alongside Giovanni, the officer of a village in the Free State of the Three Leagues. There is freedom of religion in this valley: Catholics and Protestants can live together without being persecuted, unlike in neighboring cantons. Many Catholics, however, by dint of living together with Protestants, are now used to their customs, creating a kind of 'hybrid' faith. Others, however, begin to believe that 'evil' is creeping into the valley: every little incident with livestock or harvest gone wrong is attributed to the devil, as is Sofia and Miriana's healing work.
Leonardo reports every detail to his mentor Achille who, reading the letters carefully, deems the Cardinal's presence and intervention necessary to restore order.
Sofia is warned by Officer Giovanni, who is secretly in love with her, of the coven's arrival and impending danger. His wife Lavinia, however, is pregnant and there are complications in her pregnancy, so he requires Sofia's help, who does not back down despite the complicated situation. Meanwhile Miriana becomes romantically close to Leonardo, so much so that it creates deep inner conflicts in him. Lavinia's botched birth becomes the scapegoat for accusing Sofia of witchcraft and imprisoning her. Miriana manages to escape with the help of Leonardo and the sacrifice of their friend Domenico, the village priest.