The novel takes place in Paris in 1750. In the cemetery of the Innocents, the disfigured corpse of a secular beauty was found. It soon turns out that the traces of the killer lead to the fashionable Parisian salon of the Marquise de Grammont, but Abbot Joel de Saint-Severen, who guesses about this, is perplexed: there are too many people in the salon who simply cannot be suspected, those who are suspicious of their obvious sinfulness are obviously innocent... But the detective component is not at all the main thing in the novel. Abbot Joel sees the reasons for the blasphemous abominations taking place in the new distorted thinking of people, in the quirks of the "free-spirited" mind.