Black Christmas (1974) ending / spoiler
After the killer "Billy" gets rid of the house mother Mrs. Mac (Marian Waldman), Barbie (Margot Kidder) and Phyllis (Andrea Martin), Jess gets another call. The police trace the call and realize that they are coming from inside the house (the telephone in the attic) and warn Jess to leave the house immediately and wait for them outside. Instead of going out, Jess goes upstairs with a fireplace poker and is attacked by the killer. She manages to escape and heads to the basement. There she runs into Peter, who she now believes is the killer. He approaches her to talk, but Jess kills him with the poker. The police arrive and feel the case is closed, and leave the house, leaving Jess alone to sleep off the excitement. Then as the camera shows the house we see the attic one last time and see that the two dead bodies (Mrs. Mac and Clare) have not yet been discovered. We hear a man say, "Agnes, it's me, Billy." just before the credits begin to roll, and we hear the phone ring repeatedly again.
Submitted by Big Evil