Two police officers arrive at a house and discover three of its residents lifeless. Suspecting a homicide, Officer Cobbs asks for backup. Unfortunately, Zach, the youngest child, attacks them both and kills them.
Five years later, Alyson Simon moves into a new house with her daughter, Claire. As Claire is settling into her new room, she discovers a doll hidden under her floor which has “Lilith” written on its sole. She keeps Lilith and treats it like a friend, confiding to it her thoughts, worries, and concerns.
At school, Claire draws a disturbing image of 3 dead people and someone carrying a knife. Alyson meets her neighbor, Janine, who tells her that Claire’s welcome to play with her cats and that if she needs anything, she’s just a call away. Later in the evening, as she throws the trash, she finds Janine’s cats hissing at a silhouette on one of their windows.
Claire refuses to go to school and stays home. When Alyson asks her to eat, she finds Claire singing a song while killing flies. Meanwhile, Janine goes out to feed her cats but unfortunately finds them dead.
With Claire’s drastic change of behavior, Alyson brings Claire in for a behavioral and psychological assessment. Dr Freeman tells Alyson that her separation from Claire’s father could have caused this since separation can be stressful for a child. He advises her that bringing her back to the dynamic she is used to might help.
Looking at Claire’s drawing, he says that Claire exhibits traits similar to the cases of callous children and further evaluation can determine the presence of psychopathy. At a restaurant, Claire reiterates to Alyson that she wants to go home and blames Alyson’s dedication to her career for the separation. Taken aback by her daughter's words, Alyson leaves to take care of the check.
Carol, one of the waitresses, approaches Claire and picks up Lilith. Despite Claire telling her to give it back, Carol insists on replacing it and as she turns to throw it away and get a new one, Claire screams, demanding that Carol give it back. Alyson, horrified by Claire’s behavior, apologizes to the waitress.
Grieving over her cats’ death, Janine accuses Claire as the perpetrator. Alyson denies Claire’s involvement and assures Janine of Claire’s innocence. Back at the restaurant, Carol bids her colleagues goodbye as they retire for the night.
Upon hearing utensils clash in the kitchen, she goes to investigate, yet finds nothing but a ladle on the floor. On her way back to the dining area, a knife is thrown at the wall in front of her. Horrified, she crawls on the floor towards one of the tables.
She peeks and looks for who threw the knife, yet she only sees chairs moving on their own. As she reaches for her phone, her arm gets stabbed. Failing to exit the restaurant, she retreats to the kitchen.
Unfortunately, the restaurant blows up, ending her life. Jonathan Simon, Alyson’s husband and Claire’s dad, fetches Claire and spends the day with her. He gently explains their separation to Claire.
Disappointed and feeling unloved, Claire runs away. He finds her behind a tree confiding to Lilith. As a plumber checks the house’s fittings under Claire's room floor for leaks, he finds photos of the family who formerly resided in the house and shows them to Alyson.
In the photo where Zach is holding Lilith, the plumber says that Lilith looks like a Muñeca Quitapena. When Alyson says her daughter found it and got attached to it, the plumber tells her that it’s bad luck to find someone else’s muñeca. Shortly after, she finds articles about the murder that occurred in the house they’re living in.
Alyson visits Zach, shows him the photo, and asks him why he killed his family. Unfortunately, Zach doesn’t tell her anything. On her way out, Zach sings the song Claire sang.
Alarmed, Alyson desperately asks Zach where he learned the song. Alyson calls Ken Stevens, the real estate agent who sold her the house, confronting him about the house’s history and demanding her money back, but Stevens says it’s a done deal. Furious, she calls her lawyer.
Jonathan and Claire are enjoying pizza at Jonathan’s home when Kathy, Jonathan’s friend from work and someone he has gone out with a couple of times, arrives. Claire responds coldly and dismissively to Kathy’s efforts to be close to her, even throwing away the doll Kathy gave her. Jonathan calls out Claire’s behavior and she retreats to her room.
Upset, Claire pulls her new doll’s head off its body. In the kitchen, Kathy helps Jonathan clean up. As Kathy insists, Jonathan leaves to get wine and chocolate ice cream.
Upon hearing a thud, Kathy goes to investigate what it is, checking up on Claire in the process. When the door of the empty room she just closed opens on its own, she runs frantically back to the kitchen, only to find a knife moving on its own. She retreats to one of the bedrooms and hides under the bed.
She calls 911, however, she fails to respond to the dispatcher when she sees the door opening on its own. Moments later, she gets pulled out of hiding. As Jonathan walks back to his building, Kathy falls on a car behind him, lifeless.
Alyson arrives and Jonathan tells her that with Kathy having signs of struggle, the police are looking at a possible break-in. He is in disbelief, saying he’s only gone for 10 minutes. Alyson offers Jonathan to stay with them, but he insists on staying since he has to deal with the police.
He asks them to go home since he doesn't want Claire to be exposed to such a horrific incident. Janine falls off the stairs and loses her life. Alyson later discovers her corpse.
Stevens visits Alyson at home to talk about the history of the house, but no one answers. When he’s about to leave, the door opens. He walks inside and meets his tragic fate.
Alyson discusses Claire's welfare with Jonathan on the phone, telling him that the therapy is not working. Jonathan tells her that he found the doll Kathy bought Claire underneath Claire’s bed, violently torn apart. He suggests that its absence might be for the best.
While Claire is sleeping, Alyson throws Lilith away. Claire wakes up and, furious about what her mother has done, starts breaking plates. Alyson holds Claire and tries to calm her down, explaining to her that Lilith belongs to someone else.
Claire groans in pain of her mother’s grip, revealing that she has bruises on her arms. When Alyson asks where she got the bruises from, Claire screams she doesn’t know. Later, garbage bins are collected.
En route, the garbage collector gets into an accident and his vehicle blows up. The next morning, Alyson finds Claire asleep with Lilith in her arms. Suspicious of Lilith’s involvement in recent unfortunate events, Alyson brings it to Professor Elena Carranza and tells her of its origin.
Carranza tells Alyson that it’s a worry doll. It is believed that when a child is having trouble sleeping due to stress, a worry doll worries in the child’s place so the child sleeps better. With no answers to Alyson’s concerns, Carranza asks Alyson to leave the doll so she can take a closer look at it.
Seeing the bruise on Claire’s arm, Dr Freeman asks Alyson about it, accusing her of abuse. He tells Alyson that when he asked Claire about it, she said that Alyson lost her temper and grabbed her. Alyson strongly denies the accusation and Dr Freeman clarifies that if he sees further bruising, he’ll call protective services.
Alyson calls Jonathan, telling him she doesn't know what to do anymore. Soon after the call, Claire furiously asks Alyson about Lilith’s whereabouts and her nose starts bleeding. Professor Carranza and her assistant, Ophelia, inspect the doll.
As they cut open its abdomen, Claire’s abdomen starts bleeding. Lights go out, halting the inspection, and Carranza goes out to investigate the cause of the power interruption. She comes back to find Ophelia lifeless.
In a news report, the Simons find out that Ophelia is dead and Professor Carranza is missing, which alarms Alyson. She then tells Jonathan that Professor Carranza is the one she gave the doll to. Dr Freeman watches the video of his session with Claire for further assessment.
In the video, when he left, Claire looked straight at the camera with an eerie smile. Disturbed, he pauses the video. Jane, Dr Freeman’s secretary, informs him that someone anonymously left Claire’s doll on the front door.
Alyson goes to the campus to look for Lilith, but it’s nowhere to be found. She receives a call from Dr Freeman, telling her that they need to talk about Claire as soon as possible. He tells her that he evaluated Zachary Orcutt for the court after he murdered his family and informs her that shortly after her visit to Zachary, he vanishes without any trace.
Dr Freeman finds Jane lifeless on her desk and loses his life seconds later. Alyson later arrives in a quiet office and finds DrFreeman hanging on the antler chandelier and “Lil” on the wall, written in blood. Claire, together with the doll, starts haunting her own family.
When she refuses to give the doll to her parents, Jonathan grabs the doll and as he pulls its head, Claire screams. Alyson informs him that they’re connected. Professor Carranza arrives at their house and starts incanting a prayer to trap the doll inside as soon as the family of three got out.
Claire runs back and tries to enter the house, but Jonathan thwarts stopping her and they leave. Professor Carranza confirms to the Simons that there’s a strong connection between Claire and the doll. She informs them that the connection has three stages.
First, the doll and subject are introduced. Second, the doll gets into the host’s mind and influences the host’s thoughts and behavior. Third, the doll and the host become one.
Recognizing that they're neither too late nor have much time, she emphasizes that they have to get rid of the doll the proper way. Otherwise, whatever happens to the doll, happens to Claire as well. She tells the Simons to remove the doll’s eyes first to sever its connection with Claire.
Claire interrupts, strongly opposing the plan, and runs away. As they search for Claire, Claire jumps on Professor Carranza, removes her eyes, and burns her alive. As the Simons drive back to the house, Jonathan sees Lilith sitting in the back seat in the rearview mirror.
Frightened, they almost get into an accident. They return to the house to find Lilith. Jonathan asks Claire to give him the doll, but she resists and expels him out of the room.
Claire chokes Alyson as Jonathan tries to open the door. When Jonathan finally kicks the door open, Alyson throws Lilith at him and he successfully removes its eyes, severing its connection with Claire. He steps on the eyes, destroying them.
They burn Lilith shortly after. Jonathan and Alyson get back together and they move out of the house. Claire has no recollection of the events after they moved in and Jonathan suggests keeping it that way.
As they drive away, they pass by Zachary and Claire starts singing the song.
