One cold winter night, sixteen-year-old Kelly Sanders was home alone, as her parents had gone out to a dinner party at a friend's house. It had been snowing all afternoon, but had just recently stopped. After studying for a while, she decides to relax a little - after all, she finally had the house to herself. She makes some popcorn, gets a nice warm, fuzzy blanket, and snuggles under it to watch one of her favorite movies.In their lounge room, the television is positioned a few feet in front of the glass sliding door that leads to the patio and backyard.By midnight, Kelly's parents are still not home, and she begins to feel uneasy, but refuses to call them, for risk of sounding like she couldn't take care of herself.Suddenly, her eye catches a glint of light from behind the TV, and right there, just outside the glass door, was a crazy-eyed man, grinning maliciously at her, and holding a long, narrow blade in his left hand. Terrified, the girl panics, pulls the blanket up over her head and grabs the cordless phone by her side. Kelly calls the police, and as luck would have it, there was a patrol car less than a block from her house. In a matter of seconds, two officers are on the scene and Kelly tells them about the armed man staring through the glass.The first officer opens the sliding door and looks around the area. After a few moments, she turns and explains to Kelly that there couldn't have been anyone standing out there, as there would have been footprints in the snow. The second officer tells her that she is probably just tired and her imagination was playing tricks on her. He beckoned at the TV where the horror movie she had been watching was still playing."Stuff like that didn't help matters, either,'' he said smiling.Kelly smiled too, more at her own immaturity than the officer's remark, still a little shaken.As the police are about to leave, the male officer stops and looks behind the sofa that Kelly had been sitting on. His jaw drops and eyes widen in shock. Kelly and the other officer notice his reaction and follow his gaze; they both gasp. There were wet footprints and a discarded knife on the carpet behind the couch.Kelly hadn't seen the man outside he door; she'd seen his reflection when he was standing behind her.