In 1953, Elise Rainier lives in Five Keys, New Mexico with her parents Audrey and Gerald and younger brother Christian. Elise and Christian encounter a ghost in their bedroom. Frightened, Christian looks for a whistle their mother gave him to call for help, but cannot find it. Gerald, furious, beats Elise and locks her in the basement. There, Elise opens a mysterious red doorway and is briefly possessed by a demonic spirit. When Audrey comes to investigate, she is killed by the demon.
Decades later in California in 2010, Elise works as a paranormal investigator with her colleagues Specs and Tucker. A man named Ted Garza calls, saying he’s been experiencing paranormal activity at his house. Realizing it’s her childhood home, Elise departs to help him. While investigating the house, Elise finds Christian’s lost whistle, but it disappears again after she encounters a female spirit. Elise tells Specs and Tucker that she had seen the spirit before when she was a young girl. After this earlier occurrence, Elise fled the house in fear of another beating from her father, abandoning Christian.
The next morning, Elise, Tucker, and Specs meet Melissa and Imogen, Christian’s daughters. Christian is still furious at Elise for abandoning him. Hoping to repair their relationship, Elise hands Melissa a photo of the whistle, telling her to show it to Christian. Later, Elise and Tucker discover a hidden room in the basement. Inside, guided by the female spirit, they discover a young woman being held prisoner. Ted storms into the room and reveals that he is responsible. He locks the group in and tries to kill Specs. Specs kills Ted in self defense.
Sometime later, after police clear the house, Christian and his daughters go inside to find the whistle. In the basement, Melissa is attacked by the demon from Elise’s past, known as “Key Face.” Key Face sends her into a coma, with her consciousness now stuck in the spirit realm of “The Further.”
Trying to save Melissa, Elise searches the house and discovers hidden suitcases containing belongings of numerous other women whom had been held prisoner, including the young woman she had seen as a young girl. Elise realizes that like Ted, her father Gerald also kidnapped women and held them in the secret room. The woman she saw as a young girl, Anna, was actually still alive, and was later killed by Gerald. Suddenly, Elise is ambushed by Key Face and her spirit is taken into the Further.
Imogen, who possesses abilities much like Elise’s, enters The Further with the help of Specs and Tucker. She is led by Anna’s ghost into a prison realm where Key Face is holding all of the souls he has taken, including Melissa and Elise. Elise realizes Key Face had been controlling both Gerald and Ted, and feeds on the fear and hatred generated by the women they kidnapped. Key Face tries to coerce Elise into hurting her father’s spirit as revenge for what he’s done. Elise starts beating Gerald, but is stopped by Imogen and refuses to feed Key Face any more hatred. Key Face attacks Elise, but Gerald saves her before he is stabbed by Key Face, his spirit vanishing.
Key Face stabs Melissa, causing her physical body to start dying. He attempts to possess Elise. Elise blows Christian’s whistle, and Audrey’s spirit arrives, vanquishing Key Face. With Melissa dying, they move to find her body in The Further. They open a door and see a young boy, Dalton Lambert. Realizing they opened the wrong door, they leave the door open and find Melissa in the next door. Melissa’s spirit returns to her body in the real world, saving her life. Elise makes amends with her mother’s spirit and says goodbye. Elise and Imogen return to the real world and reunite with Melissa and Christian. Christian forgives Elise and she gives him the whistle.
In her sleep, Elise has a dream about Dalton and a red-faced demon. She awakens and receives a call from a woman named Lorraine. Elise had helped her son years earlier, and now her grandson Dalton needs the same help, which Elise agrees to help.