High school student Sadie Harper and her younger sister Sawyer are struggling to cope with the recent death of their mother. Their father, Will, a therapist, is also grappling with the loss, leaving him emotionally absent as he focuses on his patients. Their strained family dynamic further deteriorates when a distraught man named Lester Billings arrives at their home seeking Will's help. Desperate and disheveled, Lester implores Will to listen to him, confessing that a malevolent entity has been tormenting his family, targeting his children. Will dismisses Lester's claim as nonsense, but the traumatic visit leaves a lasting impression on Sadie and Sawyer.

In the days following Lester's visit, terrifying occurrences begin to unfold in the Harper home. Sawyer becomes increasingly fearful of the dark, insisting that there is something lurking in the shadows. Sadie, initially skeptical, starts to witness disturbing phenomena herself. The sisters soon realize that they must confront their own fears to protect one another from the ominous presence that seems intent on plunging them into eternal darkness. As the mysterious entity tightens its grip on their fractured family, Sadie and Sawyer must rely on their wit and courage to unravel its origins and find a way to banish it before it destroys them completely.