When the novelist, Durtal, is disgusted with the modern world, Durtal goes on a journey to study the Middle Ages. While doing this research, Durtal discovers the notorious criminal Gilles de Rais. Due to his study of de Rais, Durtal discovers that Satanism is not just a phenomenon of the past but is active in his home country of France. Durtal goes on an investigation of the hidden world of the occult, and the investigation comes to a climax with Durtal witnessing the Black Mass. This novel was originally controversial when first published and remains so today. While many people rebuke the Black Mass practiced by certain groups, the reality is that the Black Mass was originally a piece of fiction from this novel that was adopted by these groups for the sole purpose of angering Christians and Christian churches. These groups succeeded in angering Christians even though the Black Mass is nothing but ridiculous buffoonery no different in genuineness than a circus show. What this novel also shows is just how little about the occult a large majority of Christians truly know, despite many who even claim to have come out of the occult and use that claim to falsely claim legitimacy in their church. Uyl provides a detailed Introduction showing how Christians do not know as much as they claim about the occult along with the hoaxers they have chosen to believe simply because ... they want to, even if what they are being told by those hoaxers is not the truth about the occult at all.