Nightmare (1980)

Original title: Cauchemar

A troubled young woman who lives alone in a rundown house meanders around and one day reveals a hidden talent when she goes into a bar, plays magnificently at the piano, and leaves as mysteriously as she came. Meanwhile, an unidentified man is on her trail and eventually tracks her down to the bar she had visited. As the dragnet around her closes in, it becomes apparent that the young woman's stepmother is behind the effort to locate her. But questions over why she is hiding out and what she is hiding from begin to take on more importance as the history of the young woman starts to surface.