Re-edit When two girls are kidnapped a psychology student believes it is the same man who took her and her sister fourteen years before. Fixated on a witness to the crime she follows and kills him.

When a kidnapping survivor, convinced of rescuing others from the same perpetrator, instead kills an innocent, she must....

Or depending on how your story goes

When a kidnapping survivor is convinced of being the only one able to rescue others from the same perpetrator, she must chase down and kill him.