Horror Film Idea

The film starts in a hallway. A guy pulls a girl along into a dark, narrow hallway (girlfriend & boyfriend). They try running but something stops them, the girl gets possessed by a demon. She stops and collapses. The guy tries to help her, and she becomes crazy. She doesn't act like herself and he notices. She then becomes violent and kills him by strangling him. Once he dies, there is a flash of the demon. She starts fighting with the demon inside of her. In the end the demon comes up to her and kills her.