As a local sheriff investigates a horrific scene where an intruder has murdered three children and their babysitter with brutal precision, a chilling sequence unfolds 125 miles away in Colorado. Here, Jill Johnson, a 16-year-old babysitter, unwittingly steps into a nightmare as she watches over the Mandrakis family's two kids after exceeding her cell phone minutes. The warm hospitality of Mrs. Mandrakis and the introduction to their live-in housekeeper, Rosa, provide her with a fleeting sense of security, especially as the sun sets and darkness creeps in.
However, Jill's brief moment of calm is shattered by a series of ominous phone calls from an unknown caller, who only emits unsettling noises before hanging up. Initially dismissing these creepy interactions as pranks from her friends, she becomes alarmed when they deny any involvement. As night envelops them and the children upstairs drift into slumber, Jill's friend Tiffany arrives for a visit. In a shocking twist, Tiffany is ambushed as she walks to her car just moments later.
The mysterious caller's harassment accelerates, taunting Jill with his unseen presence and prompting her to contact the authorities. They advise her to keep the caller on the line for at least 60 seconds to trace the call. As Jill waits anxiously, she spots a shadowy figure lurking in the guest house. Mistaking it for the Mandrakis' older son returning from college, she sets out to investigate, only to find the guest house eerily silent.
When the phone rings again, Jill is horrified to discover that the caller has switched lines. Looking out the window, she sees a light flickering inside the Mandrakis' home and naively assumes that Rosa must be there. But upon searching, she finds the house deserted. A subsequent call reveals a chilling silence on the other end. Following police instructions, Jill keeps the caller on the line and, with her heart racing, learns that the calls are emanating from within the very house she occupies.
In a state of panic, she discovers Tiffany's lifeless body slumped on the bathroom floor and races in terror back to confront the children, who are huddled together, frightened and seeking solace from the chaos. As her gaze shifts upward, she sees a terrifying figure lurking in the loft's shadows. With adrenaline coursing through her veins, Jill sprints toward the greenhouse, where her worst fears are confirmed: Rosa's lifeless body lies submerged in the water.
The assailant then emerges, their demeanor cold and methodical as they methodically search the greenhouse. In a frantic bid for survival, Jill manages to trap them inside before attempting to escape, but the intruder breaks free and launches a relentless attack. Just as hope seems lost, Jill finds a moment of clarity and ignites the fireplace, enveloping the room in searing heat that distracts her attacker. Seizing the opportunity, she retaliates by driving a fireplace poker into the intruder's hand, pinning them to the wooden floor.
Finally, with the police arriving just in time, Jill takes a deep breath of relief, watching as her tormentor is taken into custody. However, the aftermath of her ordeal takes a toll on her psyche. Days later, while recovering in the hospital, Jill's mind is still grappling with her trauma. Rising from her bed to confront her reflection in the mirror, a sudden fear jolts her, prompting a surge of anxiety that sends her reeling for the door. It’s only when she turns back that she encounters the shadow of her attacker, a manifestation of her fractured psyche. As her screams fill the room, the hospital staff, along with her father, rush to her aid, striving to pull her back from the brink as she battles to distinguish between memory and reality, past and present.
