This is Chelsea an introverted teenager and she’s quite the bookish type. Her only friend is Mia who calls her this morning to tell Chelsea that a boy named Dylan sent her a picture of him, and he wants to go out on a date with Mia.
Hearing this, Chelsea thinks this isn’t a good idea, since Mia doesn’t know him yet. Mia teases Chelsea and offers to send her Dylan’s photos. But Chelsea is wholly uninterested and tells Mia she’ll just see her at school.
Downstairs, Chelsea asks her mom to drive her to school. To her disappointment, her older and annoying sister Kristina will be doing it instead. As soon as the mom leaves, Chelsea receives a message from a guy named VR Cowboy.
Kristina takes Chelsea’s phone away and teases her, asking her if this guy is her secret admirer. Chelsea affirms she doesn’t know him and tells her sister to drive her to school already.
Upon her arrival at school, the guy texts her once more, telling her he loves her profile pics. Chelsea ignores him and goes to see Mia who’s talking to Dylan and his friend Seth.
Just as the two guys go to their class, Mia tells Chelsea Dylan invited her to come over to his house to watch a movie.
So Mia invites Chelsea, but she doesn’t like being in social situations, so she is reluctant about it.
Mia spills the beans, saying she actually wants to go there to get to know Dylan better and be close to him, while Chelsea keeps Seth busy. Chelsea tells Mia she doesn’t like Seth and she walks away.
At Dylan’s house, Dylan and Mia go to his room alone, leaving Chelsea all by herself with Seth. Trying to strike up a good conversation and break the ice. Chelsea asks Seth what music he listens to and whether or not he enjoys the movie. However, Seth is interested in her and only her, so he tries to kiss her, but Chelsea leaves quickly.
Next morning, Mia briefly says sorry to Chelsea about what happened with Seth and switches the topic to her upcoming date with Dylan.
Just then, Dylan shows up and engages in a romantic conversation with Mia.
As Chelsea takes out her phone, the guy contacts her once more. But Chelsea replies to him this time and he introduces himself as Brad. Just then, the security guard approaches Chelsea and confiscates her phone, since using phones is prohibited according to school rules.
By the end of the day, Chelsea’s mom comes to pick her up and chastises her since this is the second time she had to come and bail her out of trouble. That’s the reason Chelsea is stuck with a punishment, no phone for a whole month.
Bored, Chelsea tries to pass her time by doing anything. However, behind her mom’s back, Chelsea has Mia get her a phone. After Mia leaves to see Dylan, Chelsea starts chatting with Brad.
Chelsea tells him her name and age, and Brad notes that Chelsea’s profile says she’s a cheerleader, so he asks to see a picture of her in her cheerleading outfit. Taking advantage of Kristina’s absence, Chelsea takes a picture with Kristina’s outfit and sends some pictures to Brad.
He gets more interested in her and the two get on a video call.
However, Brad’s screen is blurry, and Chelsea can’t see his face. When Chelsea asks him about it, Brad tells her he just dropped his phone many times.
After Three weeks of chatting on the phone, Chelsea comes to admire Brad more and more. Brad tells her his parents will buy him an SUV by the time he turns 18, which makes Chelsea more interested in seeing him.
Therefore, Brad suggests she come to a warehouse Halloween party, dressing as a Zombie cheerleader, and he’ll be a zombie American football player. Loving the idea, Chelsea agrees.
By the time Halloween comes, Chelsea puts her makeup on. She hides her plans of meeting Brad, by telling her mother and sister she’d rather stay home and pass out candy to kids who step by.
After her mother and sister leave, Chelsea secretly goes to the warehouse party where she finally meets Brad. Chelsea starts wandering around. But slowly, she starts losing consciousness. Clearly, Brad spiked her drink. Brad carries her to his car and ties her up. After smashing her phone, he drives her away afterwards.
Chelsea awakes to find herself chained in a basement. Brad shows up and calls her Sadie. Although Chelsea tells him this is not her name, Brad hits her and insists that her name is Sadie.
As time goes by, Chelsea becomes more and more lonely that she even talks to a little rat, the only living being with her in the basement. Brad shows up once more and gives her some food. When Brad asks about her name, Chelsea sarcastically replies it’s Sadie.
That angers Brad, but Chelsea says sorry and promises she’ll be good. Brad drops the food all over the floor. He leaves afterwards, leaving the starved Chelsea eating her food from all over the floor.
Moments later, the rat shows up once more but is killed by a trap before Chelsea can even save it. That makes her feel lonelier, as she cries herself to sleep.
After days of being locked in the dark basement, a cheerleader named Meagan walks in and introduces herself as Sadie. As instructed by Brad, Meagan unchains Chelsea. But Chelsea thinks Meagan is here to help her, and thanks God in relief.
However, Meagan tells Chelsea that from now on her name will be Sadie, indicating Meagan works for Brad. Filled with fear, Chelsea runs and tries to escape. Much to her bad luck, the doors are locked.
Meagan catches her and warns her against trying to escape again. She takes her upstairs to meet Heather who also introduces herself as Sadie. Heather asks Chelsea what her name is, and Chelsea answers that it’s Sadie.
Heather asks Chelsea for her real name. Chelsea looks at Meagan for a moment and understands it’s a test, so, again, Chelsea’s answer is Sadie.
In order to prepare Chelsea for dinner with Brad, Meagan cleans her up and dyes her hair blonde, to look like Brad’s sister Sadie.
Meanwhile, Brad is all by himself in his room. He puts his VR headset on and starts practicing with the knife.
Chelsea hears someone hurting in the room next to hers. After checking it out, Chelsea finds a wounded girl named Tina. As Chelsea checks on her, Tina curses at her, unable to recognize anyone due to her pain.
Brad gets out of his room with the knife. Suddenly, a bad memory flashes in his mind, reminding him of how his sister Sadie bullied him. After snapping out of it, Brad takes his rage towards his sister out on Heather and slams her head against the table.
Afterwards, a bruised Heather goes upstairs only to find Chelsea asking her about Tina. Chelsea also asks why she’s not in the hospital. Heather replies that Brad won’t allow anyone out of the house.
Chelsea also asks if any of them hasn’t tried to find a way out, but Heather warns her against that, because he won’t be merciful when that happens. That’s why they start taking care of Tina by giving her some of the dinner leftovers.
Later that night, Brad has the girls enjoy some outside time. However, it’s not really outside, since they are watching the view from Brad’s VR headset.
At dinner, Chelsea breaks into tears, missing the dinners she’s had with her family throughout her life. But Brad coldly tells her to forget about them, since she has a new family now. He also tells her to stop crying on the table and have some self-control if she wants to have her dinner again.
Following their dinner, Heather starts packing up and tells Chelsea Brad allowed her to leave this house since she’s been here for three years. Chelsea tries telling her to go to the police, but Brad appears, and asks Heather to perform one last time.
Chelsea takes some of the dinner leftovers and feeds them to the wounded Tina afterwards.
At this time, Brad and Heather are on their way to the basement. A bad childhood memory strikes Brad’s mind, as he recalls how his abusive and hysterical mother always favored his baby sister Sadie over him and how she was pretty violent with him.
After snapping back to the present, Brad takes Heather to the basement. Heather starts performing, but turns around to find Brad wearing his VR headset and with a knife in his hand. Brad starts talking to her as if she’s his sister Sadie and tells her he wishes she was never born. Suddenly, He stabs her to death, while filming the whole thing with his VR cameras.
Later, Meagan talks to Chelsea through a hole in the wall. When she asks about Tina, Meagan tells Chelsea Tina tried to escape. Moreover, Meagan says she’s in love with Brad. She’s also delusional enough to think that Brad loves her.
At dinner, Chelsea empties all of the ketchup on her plate, infuriating Brad who punishes her by swapping plates with her. He also tells her not to eat, as a way of punishment for taking all of the ketchup.
The same night, Chelsea checks on Tina. It turns out Brad made her pregnant, which is why she tried to escape. But she failed at, so Brad beat her up savagely.
He also killed her baby and stabbed her in the thigh. Having lost a lot of blood, Tina can’t take it anymore. She wants to end her misery by overdosing on painkillers, which are only in Brad’s room. Chelsea refuses but agrees to help afterwards.
As Chelsea does the housework and wipes the furniture, Brad starts staring at her. Noticing that, Meagan becomes jealous and tells her to go clean something else. As she does so, Chelsea finds a picture of the real Sadie, a blonde in a cheerleading outfit, the same outfit Chelsea and the other girls are wearing.
While Brad goes outside to mow his lawn, Tina takes advantage and tells Chelsea to go and get the painkillers for her. Executing the plan, Chelsea steals the painkillers from Brad’s room and rakes the carpet to hide her footprints.
Brad is still out, so Chelsea tries using Brad’s computer to get help from the outside. Hearing Brad coming back downstairs, Chelsea quickly gets out of his room, but drops the pills all over the floor. She frantically picks them up, hides in Tina’s room.
Brad comes upstairs, and hearing Tina hurting from the pain, Brad decides to smother her under the pillow and get rid of her, once and for all. Chelsea comes out of her hiding and begs Brad to stop.
Brad grabs her by the neck and commands her to leave. Tina quietly tells Chelsea to let Brad kill her. Chelsea then begs him to let her do the killing instead, surprising Brad. As Chelsea is about to put Tina out of her misery, Tina tells her she’s satisfied it’s not Brad. Just as Chelsea starts choking Tina, Brad watches her do it in wide-eyed astonishment.
After Tina dies, Chelsea starts panting from the trauma of killing a human being. Brad is impressed and assures her it’s just the adrenaline. Brad then takes Chelsea to his room and shows her how she stabbed Heather to death while closely studying her reaction to the footage.
Deep down, Chelsea is messed up, but feigns pleasure to please Brad. Brad rewatches the video he filmed. Thirsty for another kill, Brad decides to kill Meagan by going medieval on her.
Chelsea goes along, indulges his fantasies, and suggests beating Meagan to death. Adoring the idea, Brad decides to put it into action immediately. Not wanting the blood of another human being on her hands, Chelsea distracts him and tells him she loves him, softening Brad up.
Having killed a human being, Chelsea returns to her room depressed, as she breaks down in tears.
After looking at Tina’s cold body, Chelsea is riddled with guilt. she goes suicidal and attempts killing herself by taking a load of painkillers, hoping that she’d overdose.
The following night, Brad grows fond of Chelsea. But Meagan notices that and becomes more jealous. That immediately causes some tensions between Chelsea and Meagan. So, Brad punishes them both and has them go to their rooms.
Meagan confronts Chelsea and tells her to stay away from Brad. But she tells Meagan Brad is planning to kill her. Meagan doesn’t want to believe it because she loves Brad.
Chelsea shows her Tina’s dead body, and tells her it’s Brad who smothered her. Still, Meagan doesn’t believe it. Chelsea tells her Brad killed Heather too, but still Meagan can’t believe the psycho she has a crush on is in fact a killer.
Furious, she calls Chelsea a liar. She then runs to Brad and tells him what Chelsea’s just told her, utterly changing how Brad views Chelsea. Hearing this, Brad is mad and locks each of them inside their rooms. Through the hole in the wall, Chelsea tries to reason with Meagan and convince her Brad is a killer, But Meagan demands proof.
As Brad goes downstairs with his equipment, Chelsea manages to unlock her door, and unlocks Meagan’s too. She tells Meagan about the proof in Brad’s office, the VR video.
But Meagan refuses to see it, not wanting to believe her crush is a killer. Chelsea reminds her that Brad is preparing to kill them both downstairs, so she takes her to Brad’s room and shows her the footage of Heather getting stabbed, and Meagan is shocked.
As Chelsea searches the drawers for the house keys, Brad catches them in his room. Mad that his secrets are no longer secrets, Brad locks Meagan in her room. Feeling betrayed by Chelsea, Brad ties her up and drags her to the basement, as she screams in fear for her life.
Hearing Chelsea’s screams, Meagan breaks into tears. She starts going around the room, desperately looking for a way out. She ends up breaking the wall and rushes to Chelsea’s aid.
At the basement, Brad confronts Chelsea about telling his secret to Meagan. As Chelsea pleads for her life, Brad prepares to kill her and puts his VR headset on.
Just then, Brad recalls the time he killed his mother in the basement just to be with his sister, the real Sadie. Seeing her dead mother, Sadie preferred death rather than living with Brad, so she slit her own throat and died.
This took a toll on Brad’s mental health, turning him to the psycho he is now, which explains his obsession over Sadie.
Snapping back to the present, Brad starts beating up Chelsea. Meagan attacks him with the knife, but Brad pushes her off and starts beating up Chelsea. Before he can hit Chelsea some more, Meagan stabs him in the back, decapitating him, thus allowing the two girls to steal the house keys.
With Brad out of their way, the two girls rush to the house door to unlock it. However, Brad attacks them from behind and tries to choke Meagan. But Chelsea saves her and hits Brad with own VR headset until she knocks him out.
Unlocking the door, the two girls spring out of the house to their freedom, crying for help. Encountering the neighbors, the girls tell them to call 911. Chelsea manages to call her family.
After reuniting with her family, Chelsea’s parents have her see a therapist to help her process what happened. Despite the therapist’s help, Chelsea refuses to go into details about what happened inside Brad’s house.
As for Brad, he’s locked up in a mental asylum, all alone with his inner demons.
After a while, two 13-year-old girls search online for a date and decide to lie about their age.
Getting a reply from a mysterious man, the girl rejoices and celebrates with her friend, clearly ignorant of what this guy intends to do to her.