The Millers are assisted by friends, new and old, in retrieving Flora. The horned woman's history comes to light. The season of the blood moon begins.
Matt and Shelby argue about his encounter with the horned woman (which he doesn't remember), and his secret deal to leave and destroy the house (which he does). She prepares to bathe and is attacked by the pig man, who materializes in different places around the house. The pig man chases Matt and Shelby, slashing at them, until struck from behind by Elias Cunningham. When the attacker gets back up, the professor raises his hand and banishes the creature with the word "Croatoan".
Safe now, Shelby asks Elias what Croatoan is. He describes it as a word of dark power. He explains that he has been the house's guardian for years, but was unable to afford it before it was sold to them. Matt wants Elias to leave, but Elias says that "Mr. Piggy" will return soon. He shows the Millers his records of the historic owners of the house, including the Chen family in 1973. The immigrants tried to protect themselves with folk magic, but The Butcher's group slaughtered them. The first to disappear was Edward Phillipe Mott, who built it in 1792. Matt notices the Jane sisters (Miranda and Bridget) in the clippings, and Elias details how the ghosts told him about the nurses' sacrifice at the hands of The Butcher. In 1952, three hunters killed each other. The history goes on, showing a pattern of the same lunar cycle in October: the dying grass moon. Hauntings can occur at any time, but the deaths and disappearances are in the same 6 day period.
Elias insists that they leave (since the cycle starts that night), but the Millers must find Flora first. Elias knows where they can find Priscilla. Matt and Shelby must clear Lee's name by finding Flora, who must be hiding with the ghosts of the other victims on the periphery of the land. They encounter the horned woman, and Shelby chases her. Grisly ghosts converge on them, and Shelby tries in vain to banish them with Croatoan. Elias tries to plead with Priscilla to release Flora and he is shot to death by the arrows of the Butcher's party. The Millers flee back to the house, where Cricket is waiting.
Cricket detects that Flora is still alive, but does not appreciate that they reneged on the deal with The Butcher. She is no longer willing to negotiate, as the lunar season empowers her and she's in a position of strength. Cricket leaves and is shaken after a further parlay, this time with the horned woman (named "Scáthach"). He recognizes her growing power, but he also offers Matt's sexual favors to her as a negotiating tactic. She transports him in memory to the Lost Colony of Roanoke, a community whose bounty is dependent on human sacrifice. Ambrose objected to the sacrifices to the pagan deity, saying that his mother had turned her back on the Christian God, and he led a rebellion. Scáthach detailed a plan to her. Under the auspices of a special communion of repentance, the Butcher poisoned them all and stabbed her son, killing the community and fettering their souls to the land. The last living mortal offered herself to Scáthach, who killed her, completing the dark sacrament.
Cricket relays the history to the Millers, and takes an Uber back to his hotel room to prepare for the battle that night. The driver nearly runs over a fleeing Flora.
Hours later, the Millers await Cricket's return. Matt leaves behind a sleeping Shelby to follow the siren's song of whispers to the cellar. Scáthach awaits him there, and he is unable to resist her charms. Once, the woman was an English woman who crossed centuries before. She became a new immortal goddess and a practictoner of Old Magic.
The Butcher has found Flora and is to sacrifice her in front of the Millers, but with Priscilla's help is able to escape to Matt and Shelby. Cricket, as it turns out, chased after Flora and was captured. The Butcher guts him while the Millers watch. Ambrose assists his mother in disemboweling the medium.