Dirk Renswoude is a craftsman and loner of noble birth who has been mistreated by his family. He meets Thierry, a young scholar on his way to study at the university at Basle and they soon discover that they share a fascination with the black arts. Thierry is initially cautious and afraid of blasphemy, whilst Dirk is ambitious and thirsts for power. Dirk leads them on to experiments with mystic circles drawn on the floor in chalk, the chanting of arcane incantations and the evocation of grotesque, demonic visions writhing in the speculum.