Black Christmas (1974) on Netflix

On the evening that the Pi Kappa Sigma sorority (which is headed by their house mother, the booze swilling Mrs. Mac) is holding their Christmas party, the house receives the latest in a string of obscene phone calls from who the girls call "the moaner", but who identifies himself as "Billy". Some like Jess Bradford don't like the calls, others like brash Barb Coard are somewhat amused by the calls, others like Phyl Carlson don't think much of them, and straight laced Clare Harrison is offended by them. The calls are just the latest trouble for Jess, who is pregnant and who doesn't want to tell her sensitive but volatile boyfriend, music student Peter Smythe. For this latest call, which is a bit more elaborate than those previous, Barb decides to make a snide comment in return, which provokes a threat by Billy. The next morning, one of the girls goes missing. The desk sergeant at the police station doesn't think much about this as a missing person case, especially as the police are already dealing with another missing person case (a thirteen year old girl named Janice Quaife). The police don't act until more information is brought to the attention of Lieutenant Kenneth Fuller by Clare's boyfriend, Chris Hayden. As Lt. Fuller and his men investigate, which includes placing a wire tap on the sorority house phones, more and more incidents happen to those living at the sorority house. In addition, the obscene calls continue and increasingly have a personal connotation to one of the girls, which includes information that could only be known by those involved. Or is there another reason why the caller knows so much about the specific girl in question?