The movie begins in 1953 with Elise in her childhood with her mother Audrey, brother Christian, and father Gerald in New Mexico. Gerald works as an executioner in a nearby prison. One night, moments after a prisoner is executed via electric chair, she begins to see paranormal things, including knowing the prisoner's name, family, and crime. Elise's mother speaks with Elise, telling her that while her father doesn't understand her gifts and is afraid, she can come to her for anything. As they go to sleep, her mother then gives Christian with a toy whistle and promises that any time he uses it that she will be there to protect him. They fall asleep that night and Elise hears an entity in the room, she attempts to talk to the spirit and tries to get it to come out. The spirit scares Elise and her brother, causing them to scream. Gerald comes storming in and tries to convince Elise to admit she didn't see a ghost. Elise refuses and Gerald hits her, then throws her into the basement, leaving her in the dark.While there, a demon through the red door tempts her in a child's voice to open the door, directing her to a key hanging nearby. She picks up key to open it, and a hand with keys for fingers attaches the key to its' thumb. The demon, Key Face, possesses Elise and causes the house to violently shake. Audrey goes to the basement to investigate and sees Elise shaking in front of a wall. A wire descends from the ceiling, strangling Audrey. Gerald finds his wife's dead body as Elise is released from her possession. The older Elise wakes up from the nightmare.Elise works as a paranormal investigator with her two colleagues, Specs and Tucker, taking clients via phone calls. She is called for help by Ted Garza, who has been experiencing paranormal activity since moving into his house. While on the phone he reveals that he is living in her childhood home. Hesitant at first, she explains to her colleagues what happened to her during her childhood, then deciding to accept the job in order to make things right.While in New Mexico, Elise stays in her old home with Garza. He tells her that there have been a lot of paranormal incidents happening in the home, mostly in her old bedroom, which he has blockaded and refuses to enter. Elise does a walk through the home that night, using a night vision camera so the other can see what she does. While in her old room she stumbles across Christian's whistle under their bed, which he had lost when he was six. She then also finds a set of keys in her room attached to her father's old uniform and is led to the basement by mysterious sounds where a female ghost appears only visible to the crew. When she is about to touch the ghost she jumps her from behind, steals the whistle, and shouts "help her". Elise then informs them that she had seen the ghost before in her teenage years and tells the story of a day she and Christian were cleaning the floor. Elise had heard a noise and checks the laundry room where she saw the female ghost initially. Gerald appears, but doesn't see the ghost. She pleads with him not to abuse her, and grabs his face, revealing to him that he suffers a heart attack and dies in the future. She then runs away from home and abandons Christian.Elise is then seen with her colleagues in a cafe, when two women sit down beside her. Elise recognizes them are both Christian's daughters, her nieces. Christian walks in and recognizes her, he immediately becomes upset and accuses her of lying and abandoning him with their father. Christian storms out, refusing to speak further with Elise. Elise then gives one of the daughters a picture of Christian's whistle to give it to him and to tell him that she found it in their old bedroom.That night, while exploring the house, Elise and Tucker hear the whistle being blown from downstairs. The whistle leads Elise to the basement where she realizes that it's coming from to behind a dead wall. Elise asks a series of questions and it is revealed to Elise that she'll find what she is looking for behind the wall. Elise realizes that the wall is a door and rushes to her bedroom to get the keys. When Elise opens the door, she finds a missing girl who is chained to the wall. Garza then storms in with a gun threatening them, under the influence of Key Face, and leaves to find Specs upstairs after locking them in. Specs then disarms Garza before Garza could kill him and pushes a bookcase over onto him, killing him instantly. The police arrive to rescue the girl and Elise is then brought in for questioning.While being questioned by the police Elise sees the ghost of her niece Melissa in the police station and realizes that her brother and his two daughters have gone to the house to seek the whistle because of its sentimental value to Christian. While there Melissa is lured into the basement by Key Face by pretending to be her father, which attacks her and inserts a key finger into her throat, and Key Face takes away her soul into the Further. Christian and Imogene are trying to find Melissa when Elise comes rushing there and finds her in the secret cellar room where they found the missing girl. Melissa is unconscious, bloody, and tied up in chains. Elise vows to get Melissa's soul back. This prompts Imogene to admit to Elise that she can see spirits too and stays to help Elise.Elise and Tucker go in the basement to look for the ghost and search the red door to enter The Further to rescue Melissa. Meanwhile Imogene and Specs try to find the red Bible that Garza held dear, as Elise believes it can help them. While in the basement Elise sees something in the exhaust vent of the plumbing systems and finds a night gown that belonged to the female ghost, revealing her name to be Anna. When Elise holds the gown she is able to see in a flashback that the day Elise saw Anna in the laundry room she was alive and had escaped from the cellar room where Gerald kept her, similar to Garza. When Gerald walks in the laundry room he did see Anna, but pretended that there was nothing there. Elise also sees that after her younger self had run out of the house her father brutally kills Anna. Coming out of the vision, Elise and Tucker see a string of the gown stretched and tied to a suitcase in the plumbing pipes. Tucker removes the exhaust and Elise goes in to examine the suitcase. Elise finds the belongings and skeleton of Anna inside it. When she is about to leave the pipes she hears noise ahead, going ahead to examine it and finds many more similar suitcases with remains of different people in them. While going through one of the suitcases, she is attacked by Key Face and is taken into The Further.With Elise now in The Further and captured by Key Face, Imogene goes into The Further for the first time to try and rescue her. She is met by Anna who takes her to the red door and gives her the whistle, saying she can't go past that point. Elise is then seen locked in a cage, with a collar around her neck, to relive the horror of Gerald beating her as a child for admitting she can see ghosts. She then sees Gerald being dominated by the evil entity which then presents Elise with a cane to beat him and take her revenge. Imogene finds Elise and shouts out to her, she then breaks free by telling Key Face that she will no longer hate and feed him his hatred, snapping the cane. Elise comes to realize that Gerald was the demon's puppet when she hears him use Garza's words of the entity being in his head. Key Face is about to take souls of Imogene and Melissa when Elise offers herself and it stops. Key Face then stabs Melissa, causing her body in the real-world to start dying, and then hits Elise moving to silence her voice and take over her. Imogene then throws her the whistle. She uses it, prompting Audrey to come to her aid and save them, vanquishing Key Face. She reunites with her mother and tries to apologize for her death, but her mother's already forgiven her. Realizing Melissa is dying, the trio move to leave The Further quickly. Melissa's spirit returns to her body, saving her life. Elise and Imogene return to the real-world and quickly head to the hospital to reunite with Melissa and Christian. Christian forgives Elise and she gives him the whistle, they hug and Elise leaves for her home in California.In her sleep, Elise sees a vision of Dalton and the Lipstick Demon looming over him which frightens her awake. At that moment, her phone rings. The woman on the line explains that Elise helped her son a long time ago, and that now his son, Dalton, is experiencing the same symptoms. Elise agrees to help, saying she'll meet him in the morning.