Witchcraft.

The young and fanatical Jon is appointed pastor to a remote church in 15th century Iceland. As is custom, he marries the widow of his predecessor, a woman much older than he is. He is ardent in his fight against Satan, and the villagers don't dare to question his authority. When he falls for a beautiful young woman, Jon is convinced witchcraft is at work, and his crusade leads to cruel executions of innocent people. The stronger his lust, the deeper his madness drives him in his religious fervor.