Partially paralyzed after a harrowing hit-and-run incident while jogging, Dana Milgrom finds herself enduring a challenging recovery at Hopewell Rehabilitation Hospital. Her discomfort with the hospital escalates when she suspects that someone is stalking her during the night. However, her nurse, Trevor Helms, dismisses her fears as unlikely.
During her stay, Dana's husband Steve Milgrom and their daughter Gemma Milgrom come to visit. Trevor expresses his concerns to Steve about the possibility of Dana hallucinating. On her part, Gemma has a chance encounter with the ever-watchful hospital director, Elizabeth Leaming. Meanwhile, Steve shares news about Ashley, a promising new recruit for the track team he coaches, further complicating the family dynamics.
As night descends, Dana finds herself alone again, plagued by visions of a shadowy figure that appears to be haunting her. She relays her experiences to Dr. Ron Stengel, who is intrigued not only by her claims but also by the fact that she had been clinically dead for three minutes after her accident. The situation intensifies when the ghostly figure disables her breathing machine, nearly claiming Dana's life. She tells Steve about her disturbing encounters, describing a man with an unsettling visage and elongated hands.
To mitigate Dana's fears, surveillance cameras are installed in her room. Feeling protective, Steve confronts Elizabeth about the care his wife is receiving while she admonishes Trevor regarding equipment failures he attributes to the building's faulty wiring. In a strange twist, Dana connects with invalid patient Ellie through the thin wall separating their rooms, communicating through rhythmic thumping, which offers some solace.
Determined to uncover the hospital's dark past, Dana conducts research online and stumbles upon the tragic story of Eric Nilsson—a figure linked to the hospital's history who was thought to be involved in the mercy killings of five children, ultimately leading to his own suicide in 1984. As her fears mount, Dana confronts Trevor about Eric, but he merely directs her back to Dr. Stengel.
In a fit of distress, Dana finds scratch marks on her back, believing them to be from the ghostly figure that visits her at night. In her subsequent talk with Dr. Stengel, she learns more about Eric's troubled past, including his nickname "Nails," earned from his disturbing habit of collecting fingernails from child patients, which had made him a prime suspect in their mysterious deaths. Stengel reveals that Eric took his own life in the closet of Dana's room, reinforcing her belief that a dark presence lurks within.
While on a Skype call with Gemma, Dana is devastated to discover that Ashley has been spending time with Steve at home. Just then, Nails emerges from the closet in a terrifying confrontation, but the vision dissipates when Trevor arrives in time to shield Gemma. Dana presents Steve with footage of the closet door moving on its own; however, he expresses concern that the cameras might be exacerbating her fears. Desperate for validation, Dana instructs Gemma to inquire about Nails with Ellie, but the old woman unexpectedly passes away.
In an attempt to secure their safety, Trevor nails the closet shut. Dana beseeches him for assistance to escape the hospital, but he declines, ultimately confiding in Elizabeth that he did witness something eerie in Dana's room during the rescue. As Dana’s research evolves, she comes to believe that her near-death experience has rendered her capable of seeing Eric’s ghost.
One night, Nails manipulates Dana's computer, showcasing a video that exposes Steve's affair with Ashley. To further compound her anguish, supernatural scratches etch "I miss you" across Dana's skin. In the basement, Trevor finds a file belonging to Dana Breiman. Suddenly, Nails appears once again, violently attacking Trevor and ending his life.
Steve becomes suspicious, suspecting Trevor's role in Dana's torment. Although Dana defends Trevor, she ultimately discovers that her own childhood file from when she was treated here for meningitis has surfaced in Trevor’s possession. This revelation triggers horrifying realizations, linking her past to the crimes committed by Eric.
Amidst the chaos, Elizabeth attempts to reach out to the authorities, but her efforts are thwarted by an ominous supernatural force. Tensions erupt between Dana and Steve after she reveals that Nails had shown her the video of his betrayal, leading to further disarray in their relationship. As the power fails throughout the hospital, Steve sets off in search of Ashley, only to find her possessed and ready to attack.
Realizing the impending danger, Dana urges Gemma to escape with her, fearing that Nails intends to claim more lives. With Gemma’s help, Dana bravely detaches her medical tubes and makes a run for it. In a sudden twist of fate, they come across Dr. Stengel, but he meets a grim fate as Nails kills him right before their eyes.
Determined to confront her fears, Dana locks Gemma out and faces Nails alone. In a chilling clash, Nails levitates Dana, violently hurling her around the room until she ultimately succumbs to the confrontation. As first responders find Gemma outside, she explains the horrifying truth: Nails was responsible for her mother’s death. A haunting vision reveals a ghostly Eric preparing to inject adult Dana with a needle, mirroring the tragedy faced by the children years earlier.
