Josh and Renai Lambert move into a new suburban house with their three young children: Dalton, Foster, and baby Cali. One evening, ten-year-old Dalton hears strange noises in the attic and climbs a ladder to investigate. The ladder breaks, causing Dalton to fall and bump his head, but he appears unhurt. The next morning, Dalton fails to wake up; doctors examine him in the hospital and find no brain damage, infection, or medical cause, declaring him in an unexplained coma.

Three months later, Dalton is brought home in a hospital bed. Disturbing supernatural activity begins immediately: Renai hears bizarre, whispering voices over the baby monitor, bloody handprints appear on Dalton's sheets, a trench-coated ghost walks across Cali's bedroom, and an intruder violently alarms the house. Overwhelmed with terror, Renai convinces Josh to move. They pack up and relocate to a completely different home, hoping to leave the nightmare behind.

The phenomena follow them to the new house, escalating when Foster claims Dalton wanders around at night and an apparition of a dancing boy terrorizes Renai. Josh's mother, Lorraine, visits and confesses she had a horrifying dream where a shadowy figure stood inside Dalton's room. As she speaks, Lorraine spots a red-faced demon crouching directly behind Josh's shoulder. Desperate, Lorraine calls upon paranormal investigator Elise Rainier and her tech assistants, Specs and Tucker.

Elise conducts an investigation and discovers the truth: Dalton is not in a medical coma. He is a gifted astral projector who has been leaving his physical body during sleep since he was a toddler. However, on his latest journey, he wandered too far and became trapped inside "The Further," an astral purgatory where the tormented dead roam. With Dalton's soul separated, his empty physical body acts as a beacon attracting spirits seeking to possess living flesh, while a malevolent entity known as the Lipstick-Face Demon holds Dalton's consciousness hostage.

Elise reveals that Josh possessed the exact same astral ability as a child, showing old photographs where an ominous old woman in black crept closer to Josh in every snapshot. Elise had suppressed Josh's memories to protect him decades ago. Realizing only a parent can find him, Josh agrees to be put into a deep hypnotic trance to project his soul into The Further to rescue his son.

Josh crosses over into the misty darkness of The Further, navigating past grinning, motionless spirits before reaching a gothic lair marked by a red door. Inside, he finds Dalton chained to the floor while the Lipstick-Face Demon sharpens bone claws. Josh frees Dalton, and together they sprint back toward their physical bodies while a horde of enraged wandering spirits chases them through the void. In a dark foyer, Josh confronts the shadowy Bride in Black from his childhood nightmares, shouting that he is not afraid of her before returning to his body. Dalton wakes up from his coma, completely restored.

With Dalton safely reunited with his family, Elise helps pack up her equipment while Josh relaxes. Elise notices Josh's hands look unusually withered and dirty. Suspicious, she snaps an unexpected photograph of Josh with her camera. Enraged, Josh grabs Elise by the throat and violently strangles her to death.

Hearing the commotion, Renai walks into the room to find Elise dead on the floor and Josh missing. She picks up the fallen camera, looking at the newly developed photo. The picture does not show Josh, but the terrifying specter of the Bride in Black staring back at the lens. Josh places his hand on Renai's shoulder, and as she turns around in horror, she realizes that Josh never made it back out of The Further; the old parasitic entity successfully hijacked his body while his true soul remains trapped in the dark.