Book 3. The Devil's Worshipers. A Ritual in the Name of Satan - Demon Sword, #3

After constant travels in France, caused by the direct duties of the Prelate, Rene meets Professor Fernando Sigüenza. Rene and Fernando head to Cholet together and stay at the local monastery where Rene spent his youth. In the monastery, he notices strange things. Finally, he clearly understands that in the monastery there is not a single cross, a symbol of faith, including on monks. The ghost of Isabella de Montey comes to him and tells about what happened many years ago.
The Abbot of the monastery shows Rene the protocol of the interrogation of the Marquise, hoping thereby to win him over to his side. The devil worshipers intend to transfer the soul of the Marquise to the body of the abducted Countess de Oloron. For this they intend to use the alchemical knowledge of the professorDevil worshipers are trying to perform a ritual in the name of Satan and make a sacrifice to him.
The restless spirit of the marquise burnt at the stake must move into the body of the young Countess de Oloron. For this, the countess and the representative of the Other World, the demon Arastot, must enter into a sexual relationship. But Rene de Chaperon is determined to stop them.