2011 (Nine Months Previous) - In Boston, Vivien is ready to separate from Ben and take Violet to her sister's. They discuss a house Ben found online which they would eventually live in. As they discuss it, scenes and images of events to come flash onscreen.
2011 (Present) - Ben calls out for his wife and daughter, wondering where they are. Constance has been caring for the surviving baby and is reluctant at giving him back to Ben. Vivien's sister has arrived to plan for the funeral and will be taking care of the baby. Constance warns Ben of the dire consequences of bringing the child back into the Murder House but he ignores her. It becomes apparent to him that Constance is Tate's mother. Ben is angry at her for destroying his life and threatens her.
Vivien and Moira chat about Vivien's adjustment to the afterlife. Moira tells her that Ben can't see Vivien unless she chooses to let him. Vivien believes that Ben is a good father but doesn't want him to see her or Violet in case he stays in the house. Moira reminds Vivien that they're now equals and they should be friends from now on.
Ben, distraught over the death of his family, prepares to commit suicide by shooting himself. Vivien appears and takes the gun, saying he needs to leave the house with the baby. Violet also appears, telling him the same thing. He acknowledges that the child may not even be his. The two women disappear after kissing Ben goodbye.
As Ben prepares to leave the house with the baby, he encounters Hayden in the hallway. With the assistance of the home invaders, they push Ben over the banister of the stair case and hang him on the chandelier.
Some months later, Marcy is giving a tour of the still furnished house to Stacey and Miguel Ramos. Marcy carries Hallie the dog after adopting her. They continue touring the house as their son, Gabriel skateboards around the dining room. His trip is cut short by the ghosts of Troy and Bryan. Stacey and Miguel are excited and decide to buy the house.
Homicide detectives question Constance who refuses to go back into the house after finding Ben's hanging body. The Harmons, all ghosts now, rejoice at being brought back together. Hayden refuses to hand over the living child but Travis slits her throat, handing the child to Constance. The detectives are lead to believe that Violet ran away with the child when in reality, the baby is hidden in the closet of mirrors Constance used to punish Addy with.
Violet visits Gabriel, shyly flirting with him and hinting at her ghostly presence. Tate watches on, filled with jealousy and rage.
The elder Ramos' redecorate the kitchen, and grow intimate, watched by Ben and Vivien, who are keeping their presence hidden. Miguel suggests they have another baby. Ben, Vivien, and Moira plan to avoid the family from being subject to the pain and misery brought upon by the more malevolent ghosts who only wish to inflict their fate on the living.
Miguel awakens to the sound of faint whispers. Rubber Man seduces Stacy. Gabriel awakens to find Tate sitting at the foot of his bed, and suggests he is dreaming about Violet, with whom he is still estranged. A frightened Stacy attempts to fight off the Rubber Man, while Miguel sleepwalks, and is drawn to the stove. As Stacy attempts to flee from the Rubber Man, Beau jumps from the attic, scaring her into the bathroom. Tate proceeds to fight Gabriel. Many of the spirits trapped within the house make their presence known. Gladys appears to Stacy, while a Younger Moira and a bisected Elizabeth appear to Miguel which causes him to snap out of his trance. He follows Stacy's screams to the basement. Vivien angrily guts Ben, and remarks how long she has wanted to do so. He responds by shooting Vivien in the head, with the same response. They collapse, giving the impression they are dead, and arise, urging the Ramoses to leave and never return. It was all an effort to scare them away, but Tate is not playing the same game. He actually wants to kill Gabe, so that Gabe can be with Violet and keep her company as the "normal boyfriend" that Tate could never be for Violet. He attempts to kill Gabe, but cannot bring himself to go through with it. The killer doesn't have it in him anymore. Violet stops his attempts by distracting Tate with a kiss. She wants a proper kiss goodbye, which gives Gabriel the opportunity to escape. When she vanishes, Tate begins breaks down weeping in his old room. The Harmons celebrate their success, and decide to dedicate the rest of their existence, preventing anyone else from moving in and falling victim to the house's evil forces.
The Eternal Darkness Tour now covers the Harmon history, much to the consternation of Marcy. Tate confronts Ben, pleading for his forgiveness and mercy. Ben tells him that therapy never really works anyway and calls Tate out for being a psychopath, believing that he is incapable of feeling true remorse and is only putting on an act. Tate confesses to all his actual misdeeds, which includes setting Larry on fire, killing 15 of his classmates, murdering Chad and Patrick, and impregnating Vivien. Ben can't find it in his heart to absolve him, but all Tate asks of Ben is companionship.
Vivien resumes playing the cello for the first time in a while, when she is suddenly alarmed by a baby's cries coming from within the basement. Nora rocks Vivien's "stillborn" baby, who actually lived for a few moments before dying. Nora strongly reminds Vivien the baby is hers (Nora's), and that "arrangements were made" to extract the baby from "help". Nora refers to him as, "Little Noisy Monster". Vivien quiets the baby with song, and Nora decides to take "a nice rest". She admits she probably is not cut out to be a mother. Vivien walks with the baby, trying to decide on a name.
Moira cleans the house, and Vivien shows her the baby. Moira laments that she might have made a good mother, and Vivien asks her to be his godmother.
Around Christmas time, the Harmons and Moira are seen enjoying each other's company for the first time since moving in, showing they no longer take each other for granted. Meanwhile, Hayden and Tate watch the family through the glass doors in the dark. Hayden tells him that Violet will never forgive or take him back. Tate responds resolutely that he'll wait for Violet forever if necessary.
Three Years Later (2014-2015)
Helen, a beautician, greets Constance in her salon. Constance says that she has been housebound with her newly adopted baby (from distant Virginian family). She has named him Michael. She confides that she has always known she would be destined for greatness, despite her tragedies preparing her.
When she returns home, she looks through her bloodied house to find her murdered housekeeper, presided over by a smirking and bloody Michael sitting on a chair, looking very pleased with himself. "Now whatever am I going to do with you?", she croons, showing her satisfaction as the "mother" of the prophesied "Anti-Christ".