Three months after Aunt Josephine's visit and mysterious baby Jericho's spirit's return to his body, Leanne is paranoid. Believing the cult is coming for her, she refuses to leave the Turner House. Julian, now sober and finished with rehab, accompanies Leanne on a walk with Jericho, though she is terrified. Julian tries to break up with her, but she says she likes their relationship and doesn't want Julian to change. She then mistakes a stranger for Uncle George and goes back inside with Jericho. As Julian goes to follow her inside, a chunk of the gargoyle adorning the front of the house falls off and shatters on the sidewalk, nearly hitting him. Dorothy gives Leanne a two-piece bathing suit. The next day, Dorothy, Jericho, Sean, Julian and his girlfriend Veera, leave to go to the beach, though Leanne insists on staying behind. She sits in the basement with her blank diary until the mud in the sinkhole starts to bubble. Leanne scribbles what appear to be check marks all over the page. While Leanne is cleaning, doors begin to close on their own and she hears strange noises. She drinks wine and invites Tobe over, but he is busy. Dorothy FaceTimes Leanne to check in, and she mentions Julian was attacked by a flock of rabid seagulls.

The Turners install an expensive security camera system. Dorothy hosts a mommy-and-me gathering without consulting Leanne first. Leanne hesitantly allows Dorothy to host the party. Leanne hallucinates that the camera technician has her dagger, but it is just a screwdriver. The guests arrive, including a man named Riley Smiley for the infants. Leanne is wary of him.

One of the mothers asks Dorothy a few prodding questions about Julian's prior substance abuse, and even asks about seeing an ambulance at the Turners house last summer, which was when Dorothy had carelessly left Jericho to die in the car. Leanne hallucinates that the mothers are cult members. She then discreetly checks the mothers' backs for scars while they are in downward dog, finding one peeking out of the tank top of one of the mommies. Startling her, she flies to the kitchen-only to run into Sean, who spills his blood-thickened dish on her. While upstairs washing off her clothes, she sees a mother in her room looking under her bed. Leanne confronts her, Julian and Veera come in to see the ruckus. The mother claims she was not snooping and the baby dropped the pacifier, and pulls one out of her pocket in a maneuver to make it appear she picked it off the ground. Julian tells Leanne she's overreacting.

A flashback shows Julian discovering Jericho dead in his crib, causing him to vomit. He weeps in sorrow and fear as he had tried to revive his catatonic sister. In the present, he and Veera decide that they should prove that Jericho is actually Leanne's baby. Dorothy leaves for work with blonde hair to cover a news story on a Marilyn Monroe lookalike contest. Later, Sean takes Leanne to the park. She is not as paranoid, but when Sean gives spare change to a stranger, Leanne says she wants to go home. Dorothy returns that evening and puts Jericho to bed, although Leanne isn't happy about it.

The next day, Julian meets with Roscoe. He convinces Roscoe to call in a favor to a friend of his, who will analyze Leanne, Dorothy, and Jericho's DNA. The stranger from earlier walks past the two of them. Sean brings food to her and another homeless woman, although he finds them a bit off-putting. Roscoe tells Julian via FaceTime that he needs the DNA (hair samples) within thirty minutes, and that he is visiting a relative.

Another flashback shows Julian tearfully calling his father the night of Jericho's death and asking for help. Back in the present, Julian sneaks into the nursery and pulls out one of Jericho's hairs. He searches Leanne's bedroom for her hair, but finds none. Leanne walks in on him looking under her bed. Julian attempts to rekindle their relationship and pulls out a few strands of Leanne's hair. Upset, she makes him leave.

Tobe comes with his new girlfriend Sylvia, who happens to be very rude to him, as assistants in Sean's lunch. Sylvia has donned a silver-and-red ring that will not come off. Leanne tries to tell Tobe that Sylvia does not care about him, but does not listen and returns to work. A tense situation causes Sylvia to fall and catch her ring finger on a catch that cuts it off entirely. Leanne takes little Jericho out of the kitchen as Sean and Tobe try to find her finger. Tobe accidentally activates the disposal in the drain, causing it to be destroyed. Only able to find the ring, Tobe faints.

At a block party for feeding the homeless, Dorothy ignore Julian's warnings about the cult probably watching and takes baby Jericho for his television debut to undermine her friend Isabelle for replacing her as Channel 8 reporter. Dorothy meets Nancy, who introduces herself as Sean's minister; Sean later tells Dorothy that he has been attending church services and that raising Jericho in the Church is now important to him. Dorothy responds to Sean that she has invited the Unitarian minister to dinner. Finally feeling relaxed for once, Leanne and Tobe dance and win a llama during a game. In a face-painting booth, Leanne asks for a tiger that covers the right half of her face. She overhears Isabelle and the black-haired mother of baby Matthew from the mommy-and-me group talking about the ambulance that came for Jericho's demise the previous summer. Leanne says how rude it is to talk about people behind one's back, to which the mother replies that it is just as rude to eavesdrop and leaves. Isabelle googles Leanne, and finds the missing poster that Dorothy had made before Christmas.

Sean begins his day with prayer. Leanne, sleeping in until noon, has nightmares of the night she was attacked by members of the Church of Lesser Saints. Dorothy comes into her room and is happy that Leanne is now making an effort at opening herself up more. Sean has started praying, much to the chagrin of his wife who thinks that Sean is wasting his time in "throwing the Lord down their son's throat." She prepares for the dinner party for Sean's minister friend Nancy while Sean hears yet another call from the producers of Gourmet Gauntlet. Dorothy is delighted and tries to get Sean to accept the time on the cooking show. Julian, however, reminds Sean that the last time he had left to be on that show had cost them Jericho; that accepting would unmistakably wake Dorothy up from her "sleeping beauty" routine. Checking the security cameras, Dorothy sees the attack and confronts Leanne as to why she kept her in the dark about such a horrifying experience; certain it was the cult. When Nancy finally does come, Leanne is surprisingly rude and indifferent towards her. Sean has prepared several fish dishes, having forgotten that Nancy is vegan. Dorothy arrives with baby Jericho, and notices Leanne's leg shaking due to her nervousness of their guest's presence. As they eat, Nancy brings up the time Sean was on the show "last season" which Dorothy, of course, has blocked out of her mind as it was the time she had found Jericho dead. Sean and Julian cover up her confusion under the pretense that Dorothy has "the worst memory whenever she even gets a bit jealous" and even had "forgotten her own brother's birthday three times". Leanne continues to antagonize Nancy by claiming that God would not fix her because of what she had done. Humiliated, Nancy leaves and demands that Sean stay away from her. Julian had found out that Nancy had attacked her own aging mother, who was afflicted with dementia, in 2012.

Sean's promo for Gourmet Gauntlet impresses Dorothy and Leanne. Leanne takes nine-month-old Jericho for his walk as Dorothy chastises Julian for sleeping with Leanne, to which he assures her that it is over. Dorothy tells him about Leanne being attacked and how confused she, Dorothy, is at being unable to recall Sean ever being on Gourmet Gauntlet; afraid that she is losing her mind. Julian covers this to her being under a whole lot of stress, something Dorothy takes as part of postpartum depression. At the park, Leanne sees the group of "homeless people" who present her with a necklace and tell her how Jericho is a miracle child, which implies that they are aware that Leanne had actually managed to return the infant's spirit to his body all on her own. Seeing this from a window, a thoroughly panicked Dorothy runs and takes her child. She forbids Leanne to return to the park, which Leanne compares Dorothy's controlling nature to May Markham's. Sean disregards Dorothy's increasing paranoia regarding Jericho's safety as he prepares dinner and she leaves upstairs. Leanne tells Sean that the homeless people she has visited appear to almost worship her to the point of wanting to learn from her rebellious nature for being able defect from the Church of Lesser Saints cult.

Leanne takes on a leadership role with the homeless encampment, whose inhabitants seem to be runaways from the cult. At home, Dorothy is cold toward Leanne and refuses to let her touch Jericho, as well as making Sean sleep on the couch for as long as he refuses to kick Leanne out. Isabelle starts showing up near the house and speaking to Leanne, offering to befriend her and bond over their shared grievances with Dorothy. Isabelle later calls an ambulance on a homeless man she claimed was sleeping nearby, and Leanne spots her speaking to a paramedic and pointing at the Turner home.

Dorothy asks Leanne about her smiling at Isabelle's death, and Leanne says that Isabelle only wanted to hurt Dorothy. Leanne and Julian have sex on the back patio, unaware that Dorothy is watching them on the security camera; Dorothy later confronts Julian, who suggests she make peace with Leanne. Dorothy, meanwhile, continues to refuse to let anyone other than her, including Sean, hold or care for Jericho. When Dorothy refuses a breakfast cooked by Sean and instead has cereal, she finds insects in the cereal bowl. Later, when Leanne leaves to go to the park, Dorothy looks through her belongings and sees a drawing of her whipping herself with a drop of blood on it. Dorothy sees the same scars on her back and asks Leanne about them, but Leanne insists she does not hurt herself or listen to the cult any more. Dorothy convinces her dad to bring a psychiatrist friend of his to the house to evaluate Leanne for commitment. The doctor speaks to Leanne and Dorothy each by themselves.

When Dorothy wakes up the following morning after being given trazodone, Sean and Julian show her support against her father's actions. Leanne tells Dorothy that she is going to help her no matter what, says that she forgives her for trying to get her sent away, and pleads her to stop fighting her. Dorothy appears to accept this and starts to act more friendly towards Leanne, but Sean and Julian both do not believe it to be genuine. The next morning, Leanne takes Dorothy with her on her walk into the park with the "homeless people". There, Leanne tells Dorothy of a new job opportunity as an anchor that one of her friends found, but Dorothy doesn't believe they'll accept her. Later in the tub, Jericho says "mama", his first word, seemingly to Dorothy. However, Dorothy then realizes that Jericho was looking over her shoulder, possibly speaking to Leanne. Dorothy cooks dinner that night for herself, Sean, Leanne, and Julian, and they all seem to be in good spirits.

Leanne prepares the house to welcome a paraplegic Dorothy when one of the Church of Lesser Saints cult members attack her by spaying her eyes with holy water.

Dorothy hires two live-in nurses to accelerate her recovery and protect her from Leanne. One of them, Roberta, is a spiritual medium who conducts a séance to help Dorothy finally heal by beginning to accept what has happened to her and move forward. It is during this ritual that Bobbie hears a baby (Jericho) crying, wondering why no one comes to help him. Leanne presents the dagger that she procured in the third season and attacks Bobbie under the assumption she is hiding scars as proof of flogging by the Church.

Dorothy is further agitated upon discovering that Leanne's coming to their home was no coincidence. Sean and Julian are visited by George who finally reveals "the truth" about Leanne, claiming that she is just an ordinary young woman who has had a psychotic obsession with Dorothy since that 2011 beauty pageant interview; that Leanne had particularly chosen Dorothy as the loving mother she never had. He assures Sean and Julian that the loss of taste Sean had last fall and winter was merely Leanne putting a certain pill in his dinner, and that Beverly had died from a snakebite at the petting zoo birthday party.

To top it all off, George finally reveals that the "Jericho" the Turners have had since early September 2019 is, in actuality, the child of a deceased homeless drug addict whom Leanne had found and had been passing off as Jericho ever since, having been snuck in and out through a hidden tunnel whenever Leanne saw fit to torment the Turners further. Sean and Julian are thoroughly stumped by these revelations as they contradict all of their suspicions of Leanne being a supernatural being whom they earlier referred to as a reborn "fallen angel" as a byproduct of the Faustian Bargain tale.

Sean and Julian now come to a final decision, and confront Leanne about the psychotic influence she has had on their lives as a sudden freakish downpour comes down on all of Philadelphia; something that people at the news station think is just a freak act of Mother Earth and nothing more. Up in the attic, however, Leanne knows otherwise. Now using a walker, a gradually recovered Dorothy hears a noise from Jericho's bedroom, which puzzles her as she has her young son next to her in his crib. Finding the window wide open during such a heavy rainstorm, she comes to close it and is unnerved to see Leanne so calm and meditating. Leanne again asks Dorothy why it is so difficult the like her, to which Dorothy wonders to why did Leanne seek only her attention and approval out of all the thousands of people in Philadelphia. Leanne dodges the question and informs Dorothy that even Sean and Julian no longer like her and that she feels all alone.

Downstairs, Sean and Julian are talking about best it is to get Leanne to where her "uncle" awaits to take her back to where she belongs. Convinced that the rainstorm is for her alone, Leanne laughs in the face of "Him", wondering if that is all he has got against her. Julian finds her and attempts to have her come with him to see something, which Leanne finds suspicious. Julian then grabs Leanne and calls out for Sean who manages to knock her out. They have Leanne bound and gagged in Dorothy's wheelchair and present her George and two other members of the Church of Lesser Saints. Confident that they have finally rid themselves of Leanne once and for all, Sean and Julian leave her at the mercy of her former cult members. With the red-hot dagger ready, George tries to persuade Leanne to set the Turners free by ending her own existence as he is fully aware that the cult has been unsuccessful in doing so as they know just how dangerous and strong she really is. However, Leanne turns the tables on her uncle by running him through with the fiery dagger and leaves George and the others to burn in hell by completing the ritual herself.

After Leanne calls Sean at the hospital and threatens his life, Sean and Julian try to arrange a meeting outside the house with Dorothy, in the very backseat where Jericho died, who is alone with Leanne. Dorothy is able to sneak out and meet them in their car, where they attempt to remind her about her actions that unintentionally led to Jericho's premature death.

Dorothy wants to be alone, but Sean and Julian object, as they know what Leanne is capable of, still under the belief that Leanne has just hidden away the infant boy of another grieving family two states away, to which Dorothy assures them that there is no infant in the house. She tells them to go back to the car and wait for her. A desperate Leanne continues to plead with Dorothy to accept her, but Dorothy merely ignores her as she goes to mourn in Jericho's room. Furious and heartbroken, Leanne goes to the roof and screams at God for refusing to let her have what she has ever wanted: Dorothy to love her as a real mother would.

As the rainstorm worsens, Sean's stitches reopen and Julian is ready to drive him back to the hospital. Dorothy finds a distraught Leanne and tries to get her to come back inside. She assures Leanne that she is not evil, as she had given her months with Jericho when she would have done anything to have her son if only for just one moment and that was more than enough as she had to live with the pain of losing him as part of her deep love for him. Leanne, however, contradicts her, saying how as a girl, she had hid in her room with the fear that she would be punished for the fire that had killed her parents thirteen years ago. As more lightning strikes, Leanne saves Dorothy, and they return to the house. Leanne assures Dorothy that Jericho forgives her for, which leaves Dorothy in relief. Dorothy then gets in the car as Sean has to be taken to the hospital again due to his stitches coming loose. Inside the house, Leanne had started a fire by dousing the rooms in gasoline and throws down a lit match and calmly watches the reborn doll burn to ash. Putting on a Vivian Dale song, she calls Tobe who again asks her out. Leanne says that she would really like that and assures him that it will not rain tomorrow. Having a final conversation with the mannequin she sees as her late mother Laura, Leanne assures it that she has a new mother now and that she no longer needs anything from her, though she does wonder what it feels like when one burns to death. As everything is engulfed in flames, Leanne undergoes the ritual by blinding herself with perfume and slitting her arms with the dagger she had taken from George's corpse. Not wanting to wait any longer, Julian is shocked to find the entire house afire and notices Leanne's shoes outside as she jumps into the flames.