Home alone one night, SARA, 22, receives some seemingly prank calls from a mysterious male voice. Prank, that is, until the caller tells slip that he knows her name. After a few hang-ups, she goes to bed but hears a noise from downstairs. She arms herself with a baseball bat and goes to investigate... but instead of finding a bloodthirsty killer... she only ends up hurting her best friend (and total flirt), JJ.
After drinks and traded stories, the mystery man calls back, and JJ answers the phone, but even she is creeped out enough that she ends up hanging upon him. When the caller rings back a third time, he does so with a message for Sara: "Look in your mailbox". In the mail, Sara finds a newspaper clipping of her parents' murder and realizes the caller is their killer, Cyrus.
Wasting no time, Sara calls the police only to find they're busy at the local prison trying to stop escapes after a riot. The only cop available is the operator.
Sara and JJ get in the car in the garage but the engine has been tampered with and Cyrus rolls out from under the car. After a fight, Sara and JJ escape and the cop arrives on the scene to help them... but he is quickly killed with his own weapon.
The girls barricade themselves in a bedroom and argue over what to do. JJ wants to call someone else to help them but Sara refuses to risk anyone else's life. JJ realizes no one is coming and tries to think up escape plans, but Sara pokes holes in everyone, frustrating JJ into mistrust.
When Cyrus calls back, Sara makes JJ keep him on the line phone as long as possible while she sneaks out of the house to get the keys from the dead cop's body. Cyrus tells JJ about how Sara left her own mother to die and offers her a deal: Let him in and live, don't and die. Sara finds the keys and the cop's radios goes off. Cyrus finds her but she manages to escape.
Sara is ready to make a break for it but JJ isn't as trusting of her any more following Cyrus' revelation. Sara revises an old idea of JJ's for them to try, JJ agrees and Sara goes to the bathroom. Cyrus makes himself known at the back door window to let JJ know he heard their plan. JJ cries and ends up dialing *69.
When Sara returns from the bathroom, she finds Cyrus in the kitchen with a knife to JJ's throat and a gun to her temple. Cyrus reveals to JJ that after killing Sara's father, it was Sara who killed her mother, not him. He made her do it in a deadly game. He proposes a similar game but Sara refuses, hits him with a kettle, runs upstairs and barricades herself in her room. Following, Cyrus breaks through the door and Sara knocks him out the window then storms outside to finish him off... but he's not there.
Untrusting and fearful, JJ locks Sara out of the house and Sara runs for it. Eventually, Sara is found and captured trying to escape over the back garden fence. Cyrus hurts Sara badly and is about to kill her when he is shot by JJ with the cops' gun.
As Sara and JJ makeup and head back to the house, Cyrus rips open his jumpsuit to reveal the cops' bulletproof vest. They don't see him approaching.