This is one disturbing film. It focuses in on a young woman, Carol, who is a bit unhinged. She starts off being guarded and recluse, then she progresses into a full out paranoid state of mind. It's really unnerving to watch. She cannot stand that her sister is having an affair with a married man, but things become worse for her when her sister leaves her at the apartment by herself to go on vacation. Even though Carol is old enough to be alone, she is struggling so much mentally that it ends up being a poor decision to leave her alone.
When alone, Carol is very frightened. She imagines footsteps in the hallway, strange men in her bedroom, and cracks in the walls. She ends up getting to a point where she does not leave her flat and she is always wearing her nightgown. This movie has a slow start, but once she starts losing her mind, it becomes very interesting. I was very freaked out by this movie by the end.