To cover the cost of her excess cellphone minutes, Jill Johnson (Camilla Belle) agrees to babysit for an affluent family. Upon her arrival at their lavish home, she is welcomed by the parents, who inform her that they will not be back until midnight. They also mention their live-in housemaid, Rosa, who takes care of various household duties.

Once the two children are tucked in upstairs, Jill unexpectedly starts receiving anonymous phone calls from an unknown caller. Initially thinking it might just be a prank from her friends, she soon realizes that the situation is more serious when her friend Tiffany ([Katie Cassidy]) drops by. Jill is too anxious to have Tiffany stay, fearing repercussions, so she asks her to leave. Unfortunately, Tiffany faces an unseen danger outside as she heads back to her car.

Soon, peculiar incidents unfold around the house—like the security alarm going off for no apparent reason and whispers at the door without anyone present. Just then, the unsettling caller asks Jill, > “Have you checked the children?”. After she acts on his disturbing suggestion, he calls again to inquire, > “How were the children?”, revealing his chilling ability to watch her every move. Terrified, Jill contacts the police, who instruct her to keep the caller on the line for sixty seconds to trace the call.

While waiting anxiously for another ring, she notices a shadow moving in the guesthouse. Thinking it might be the Mandrakis’ son returning from college, she investigates but finds the guesthouse deserted. Returning to the main part of the house, Jill searches for Rosa but only discovers her belongings, creating a deeper sense of foreboding. When the phone rings again, the caller remains silent, but Jill manages to hold the call long enough for the police to trace it.

As the tension escalates, she hears water running in the maid’s room but finds the bathroom empty. The police then reveal the chilling truth: the calls are coming from inside the house. Panic-stricken, Jill discovers Tiffany’s lifeless body on the bathroom floor and hurriedly seeks the children, who are secretly hiding in their playroom. Just when Jill thinks she might have secured safety, she spots the intruder lurking in the loft.

In their frantic escape to the greenhouse, Jill uncovers Rosa’s corpse submerged in the water, heightening the sense of dread. As the predator prowls through the greenhouse, she manages to trap him momentarily but he ferociously breaks free and confronts her. In a desperate struggle, Jill stabs the attacker’s hand into the floor using a fireplace poker, making a narrow escape into the arms of a police officer.

Days later, Jill awakens to the sound of a ringing phone. As she rises from her bed and glances into the mirror, the shadowy figure of her assailant suddenly appears behind her, leading to a terrifying confrontation. In a disorienting moment, she awakens from this nightmare to find herself in a hospital, where her father and the doctors work to calm her from her hysteria. The screen fades to black, leaving viewers unsettled as the chilling narrative comes to an end.