Sara Dunn's life is a complex tapestry of uncertainty, marked by a strained relationship with her mother that looms over her existence. As a high school student without a stable home, she often resorts to taking food from her mother’s house and spends nights either at friends’ places or under the stars. This precarious lifestyle leads to chronic sleep deprivation, rendering her unable to concentrate during classes and throughout her daily life. To make matters worse, she is plagued by vivid, surreal nightmares where she navigates through a confounding maze, haunted by a terrifying figure with ember-like eyes.
In a bid for financial stability, Sara decides to participate in a sleep study, although the true aims and details of the experiment are kept shrouded in secrecy. While she initially experiences peaceful slumber, her nightmares grow increasingly unsettling after just two sessions, intensified by a mounting sense of dread. Compounding her anxiety is the revelation that Riff, one of the young researchers, has been tracking her activities outside the study, and the sole other female participant, Emily, seemingly vanishes without explanation. Sara’s stress escalates dramatically when a researcher presents her with a photograph of the shadowy figure from her dreams, triggering a panic attack and utter frustration at the scientists' opaque intentions. In response to Sara's acute distress, the lead scientist, Dr. Meyer, steps in to halt the unapproved practices of the younger researchers.
As tensions rise, Sara grapples with a terrifying encounter at a local laundromat that leaves her phone stolen and amplifies her urgency for answers. She confronts Riff, expressing the detrimental effects of the study on her health and demanding clarity on its purpose before she continues as a participant. Riff eventually unveils a shocking revelation: the study involves monitoring dreams through a state-of-the-art brain scanning device, which translates brainwaves into visual data.
During her next session, Sara and the remaining participants experience a joint nightmare that features the same ominous figure, resulting in synchronized spikes in their vital signs. Riff opens up about his own childhood terror associated with the entity, indicating that this dark presence has stalked individuals throughout history. As Sara jolts awake in panic, her left eye bleeding, she escapes Riff's grasp and runs toward a local club where she hopes to find her friend Zoe. Weariness catches up to her, and she collapses, prompting Riff to carry her unconscious body through a bustling street.
As the other participants begin to succumb to the malevolent force enacted by the shadowy figure, their minds get ensnared in a quagmire of sleep paralysis, compelled to face the darkness plaguing their dreams. The scientists are left reeling as the entity's grip begins to extend into the waking world. When one researcher dares to enter the volunteers' quarters, the figure reaches out, inducing shivers and causing the monitoring equipment to malfunction.
Sara's own spiraling descent into nightly terrors intensifies when she finds herself in Riff’s apartment, only to uncover his unsettling habit of self-monitoring his dreams. Here, she inadvertently witnesses a terrifying dream where they transform into fanged creatures, sharing a twisted kiss. But the unsettling experiences don’t end with Riff; soon, Sara is ensnared in her own dreadful visions, forcing them both to confront their shared darkness. Overwhelmed by their respective traumas, they come together, seeking comfort in each other’s arms amid the chaos.
While Riff anxiously awaits updates on Sara's condition, his own dreams spiral into a frenzy, haunted by images of a labyrinthine maze and the stalking humanoid figure. The situation reaches a critical point when he learns of Sara’s escape from the hospital, her eyes bleeding as she sleepwalks through the city, revealing the extent of their shared anguish.
Riff’s colleague, Anita, soon joins him as they deploy a mobile monitor to track Sara's wandering form. Their journey into the woods uncovers that Sara's dream is ominously aligning with their path, as shadowy figures emerge on the monitor. Suddenly, when Riff stumbles upon a forgotten cellphone, the ringing interrupts the unsettling silence and pulls Sara back to consciousness.
As Riff tries to comfort his frightened friend, Sara shockingly claims ownership of the phone, even though they are in an unfamiliar location, suggesting a disorienting connection to her experience. Fleeing from the approaching darkness, it's revealed that Sara has become increasingly unable to direct her own actions. The screen on her phone shudders with static, indicating that though she is awake, she remains beset by haunting visions of shadowy apparitions in the trees.
The trio's flight quickly turns to despair when darkness claims both Anita and Riff, leaving Sara standing helplessly as the very entity she has been fleeing advances upon her. As Sara's consciousness stirs in Riff's apartment, she finds herself entwined with his lifeless body, confronting the horrifying aftermath of their ordeal. The eerie silence is broken by the rustling of her own skin as she begins to comprehend the surreal scene before her. In a moment of introspection, she discovers a cryptic message on her phone, triggering a wave of morbid intrigue as it starkly reveals that two decades have elapsed since a devastating accident landed her in a coma, where scientists turned their attention to studying her dreams through revolutionary new methodologies.
As the staggering realization sinks in, Sara catches a glimpse of her own reflection, only to find an unfamiliar face marred with the ominous presence of fangs. The chilling message on her phone compels her to awaken, leaving her grappling with an existential crisis as the screen fades to black, hinting at the consuming shadows that threaten her very essence.
