The human hunter, who gave his life to pursuing the servant of Satan, did not realize that only one who becomes a demon himself can defeat the demon. The action of the novel takes place in an alternative world, similar to ours in the second half of the 17th century. The only differences are some geographical features. For example, instead of the Holy Roman Empire, there is the Kingdom of Germany, approximately within today's borders. England and Scotland have not yet united. There was no Reformation, and the Catholic Church still maintains a strong position in world politics. There is also the Holy Inquisition, but its affairs are mostly secret and relate not only to heresies.