Lurkers (1987)

Cathys mother killed her father and tried to kill her when she was ten. Her younger brother, a priest, holds her responsible. Fifteen years later Bob manipulates a clingy, drippy Cathy into falling in love with him. He lures her back to the apartment building of her youth for a so-called work party. There, he and his business partner Monica and a few of their oddly pathetic friends hold Cathy hostage for a few hours before forcing her off the side of the building roof. She becomes one of them, a 'lurker'. The building is supposed to be 'hell' and everyone born there is evil and is brought back there to die. Cathy becomes one of the lurkers who floats around town warning other people who the baddies try to get back to the building - Bobs new girlfriend and Cathys priest brother including.