That’s pretty funny, the movie poster giving away one of the big secrets of the film like that. Sisters is a Brian De Palma film from early in his career. It cribs heavily from Hitchcock, especially films like Rear Window and Psycho, but there’s also a touch of The Snake Pit in there for good measure.
A journalist witnesses a murder in another apartment, but the police don’t believe her because she has written about police brutality. So she investigates on her own and discovers the woman in the apartment was a conjoined twin who was separated. Her sister died, and she went crazy as a result, developing a murderous split personality representative of her deceased twin. That, and the guy she claims is her ex-husband is also her doctor, accomplice, and really is her husband.
In short, the film is kind of a mess. That’s not to say there isn’t some interesting stuff going on, particularly regarding voyeurism, as well as depictions of interracial sex, racism in the police force, the growing divide between views on women in the work place of the Greatest Generation versus the Baby Boomers, the power of hypnotism, and cake decorating. Oh, and it turns out you can stuff a dead guy in your sleeper sofa and nobody will notice. But the killer twin/mental illness thing just doesn’t do it for me, and I would have much rather focused on many of the other ideas that popped up. Those would have been much more interesting to me, particularly cake decorating.
Some folks like this movie. I feel kind of ‘meh’ towards it, mainly because I find the plot bizarre and overly convoluted. If I really want a decent Hitchcock knock-off, I’d rather go watch Peter Cushing in 1968’s Corruption. But maybe that’s just me.