A dangerous psychopath hiding out in the attic of a sorority house torments a small group of pretty young sisters (including Olivia Hussey and Margot Kidder) who are staying behind over Christmas break. His tactics range from making obscene phone calls from their house-mother's phone, to stalking the terrified boarders with sharp objects and murderous intent. Director Bob Clark demonstrates a tight, aggressive style that generates some very original shocks -- particularly the surprise ending -- which clearly influenced dozens of similarly-themed slasher films to follow.