This underrated holiday horror pre-dated the Halloween slasher cycle and practically established the genre's hard-and-fast rules. A maniac is on the loose in a closed-for-Christmas girls' boarding school in director Bob Clark's neat little chiller, which scores thanks to its stylish visuals, fiendishly inventive slaughter and unexpected twists. Promoted at the time with the wicked tag line "If this picture doesn't make your skin crawl, it's on too tight!", the film also features above-average performances from Olivia Hussey and Margot Kidder. Clark went on to direct Porky's and the minor yuletide classic A Christmas Story.

As the residents of sorority house Pi Kappa Sigma prepare for the festive season, a stranger begins a series of obscene phone calls with dubious intentions...