This cult classic exists on the intersection of campy tabloid-style soapyness - painting its protagonists with rather broad strokes and even fitting in a love interest as kind of a comic relief character - and, for its time, a rather forward-thinking psychological layer elevating this thriller above what could've turned out a mediocre piece of melodrama fluff - and which also would have fallen completely flat if it weren't for the valiant performances of its two lead actresses. Kinda as if Sunset Boulevard's delusional Norma Desmond character got thrown into a co-dependent sibling rivalry kind of relationship - an early depiction of what might be diagnosed as narcissistic personality disorder today, while giving the audience quite a few clues (and in its final moments, confirmation) that beneath the innocent and forgiving demeanor of the "good" sister, there are plenty of skeletons lurking in the closet as well.