The priest, Father Dominic, arrives in the small town and befriends the miller, Joseph, and his son, Jacob. He observes their daily activities and notices that there is nothing unusual about their behavior. However, he becomes suspicious when he overhears Joseph talking about finding water in an area where nobody else could.
Father Dominic starts questioning the townsfolk and learns that Joseph and his family have been accused of practicing witchcraft. They are rumored to have supernatural powers that allow them to control water and predict the future. Father Dominic also hears about a mysterious fire that destroyed the miller's ancestral home, and thinks that it might be connected to their alleged witchcraft.
As Father Dominic investigates further, he discovers that the miller's family has been keeping a dark secret. They possess a rare book known as "The Grimoire", which contains instructions on how to summon demons and make pacts with the Devil. The miller's ancestors used this knowledge to ensure their survival and prosperity, but the current generation has never used it.
Father Dominic becomes convinced that the miller's family is indeed in league with the Devil and decides to confront them. He goes to the miller's home and demands to see the Grimoire. The miller and his son refuse, claiming that they have never practiced witchcraft and that the book is simply a family heirloom.
Father Dominic, however, is determined to uncover the truth and starts to ransack the house. He eventually finds the Grimoire hidden in a secret compartment, but as he reads through it, he realizes that he is in grave danger. The book contains spells that could summon demons and unleash unspeakable horrors.
In a heart-pumping finale, Father Dominic must race against time to save the town from the impending demonic threat. He must also face the consequences of his own actions and question whether his blind faith has led him astray.