A teen boy goes to the basement of the house and looks into a fireplace or boiler or something. A voice talks to him, it's the devil. He becomes possessed and a preist tries to help him. He tries to kill his sister in the movie. The voice keeps telling him to kill people. The very end of the movie the boy and the preist have a fight and then the boy can't remember anything after he is not possessed anymore. The movie was 1980's
