On Halloween, the one day in which the dead can walk the earth among the living, Violet learns that Tate is an infamous school shooter, who killed a library full of his fellow teenagers (as well as crippling a teacher and setting Larry Harvey on fire) as a ploy to punish his mother Constance for having Tate's younger (and deformed) brother euthanized. Addie is run over by a car, leading to Constance failing to get her corpse moved to the house property to imprison her spirit so that she can be reunited with her brother's ghost. Vivien meanwhile learns from the "Murder House Tour", that the house was the home of a back alley abortionist and that the monstrous ghost in the basement of the house is the ghost of the doctor's son, who was killed by a patient's vengeful boyfriend and resurrected as a monstrous "Infantata" monster.
Faced with the monster Tate is and her own romantic feelings for him, Violet kills herself, something she doesn't realize was successful until weeks later when she realizes she cannot leave the house. Tate convinces Violet to lie and help her father commit Vivien to an insane asylum, as Ben is convinced that the second father of her child is a neighborhood security officer. Meanwhile, Constance enlists the help of a psychic (Sarah Paulson) to help her talk to Addie; when Violet realizes that Tate had sex with her mom and encountering the gay couple, who she discovered was murdered by Tate, she breaks up with him and tells Constance about what Tate did. Constance discovers from the psychic, to her horror, that Tate's child with Vivien will become the Anti-Christ. When Moira and Violet tells Ben the truth about her being a ghost, Tate being the "rubber man", and the evil in the house, he has Vivien freed from the asylum.
Now trapped in the house, the Harmons (Vivien, Ben, Violet, and the deceased twin) team up with Moira to keep further families from the house by fake haunting the place every time it is sold. Tate meanwhile has consigned himself to living with Hayden, both of which have been blocked out by the Harmons using a trick that Tate taught Violet when she first died. Elsewhere, Constance (who left town to create a cover story regarding the Harmon child she is now raising) returns to Los Angeles but finds that her grandson (The Anti-Christ) has murdered his nanny, after returning home from getting her hair done. She slowly walks to the young smiling, giggling boy. She then smiles and touches his hair and whispers "Now what am I gonna do with you?"