The film opens with Paul ('Billy Burke') engaged in an unsettling late-night Skype conversation with his son, Martin ('Gabriel Bateman'), amidst his work at a mannequin factory. During their discussion, Martin expresses his concerns regarding his mother, Sophie ('Maria Bello'), whose strange behavior has become increasingly alarming. Paul tries to reassure Martin, expressing his belief that things will improve in due time. Meanwhile, as the night progresses, Paul's assistant, Esther ('Lotta Losten'), begins to secure the warehouse for the evening. While carrying out her routine of turning off the lights, she becomes aware of a menacing presence lurking in the shadows. With each flick of the switch, the figure seems to vanish, but on her fourth attempt, it looms ominously close. In a panic, she rushes to inform Paul, but he dismisses her fears and sends her home.
As Paul readies himself to close the warehouse for the night, he recalls Esther's frightful account and hesitantly ventures into the dimly lit space. It isn't long before he encounters the haunting figure lurking in the darkness. Just as he realizes its presence, a motion-sensitive light fails to stay lit, submerging him into near-total darkness. Desperately waving his arms to reactivate the light, he suddenly sees the figure closing the distance. Panic-stricken, he hurries away, but not before the creature manages to claw at his leg, injuring him. Understanding that the figure thrives in shadows, Paul rushes to his office, arming himself with a baseball bat as he locks the door behind him. Suddenly, the lights flicker out completely, and the figure attempts to force its way inside. Just as the door opens slightly, Paul is violently yanked into the abyss, leaving only his lifeless body behind.
Days later, Martin overhears his mother conversing with an indistinct entity during the night. Troubled, he approaches her room, only to witness Sophie speaking to a shadowy figure in the bathroom. When Sophie notices him, she offers an apology, seemingly unaware of the palpable fear engulfing Martin. After that disturbing episode, he returns to his room, where he is met by rattling doorknobs and more unsettling sounds. Meanwhile, across town, Martin's sister, Rebecca ('Teresa Palmer'), is with her boyfriend, Bret ('Alexander DiPersia'), but the next day, she receives a concerning call from school about Martin's erratic behavior and insomnia. alarmed, Rebecca confronts their mother regarding her neglect of Martin, especially since Sophie has been refusing to take her antidepressants, escalating tensions within the family.
Back at Sophie's home, Martin comes clean about his mother's conversations with someone named Diana. Concerned, Rebecca tries to reason with Martin, asserting that Diana is merely a product of their mother's imagination. Following a heated argument with Sophie, Rebecca takes it upon herself to take Martin into her care for safety. However, as night falls, they both awaken to find Martin missing. In a frantic search, they unwittingly uncover the sinister entity that has permeated their lives.
Delving deeper into their mother's past, Rebecca learns about the tragic life of Diana—an unfortunate girl who was unable to withstand light and ultimately became a dark, vengeful specter. As Diana emerges to threaten Rebecca, it becomes horrifyingly clear that the darkness is her greatest ally. After a series of chaotic confrontations with the entity, Rebecca realizes that the only way to end this torment lies in breaking the hold Diana has over Sophie. Ultimately, during their confrontation, Sophie recognizes the imminent danger and makes the painful decision to confront her past along with Diana, resulting in her own self-sacrifice. This critical choice allows her children to escape the wrath of the vengeful spirit, leaving Rebecca and Martin to grapple with their profound loss while trying to reclaim the fragments of their disrupted lives.
In the aftermath, Rebecca emerges from the harrowing experience, but she carries the weight of both physical and emotional scars, as the shadows of darkness continue to echo ominously in their lives.
