Sisters

Sisters (Criterion #89). 1973 American International Pictures & Janus Films.
Starring: Margot Kidder, Jennifer Salt, Charles Durning, William Finley, Lisle Wilson
Director: Brian De Palma
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Two paid actors (Kidder & Wilson) appear on a game show called Peeping Toms, which honestly wouldn't be out of place in today's television lineups. Danielle and Philip go out on a date after the taping, and things are going nicely until her creepy ex-husband Emil (Finley) shows up at the restaurant. He's stalking Danielle, so they have to sneak back to her apartment on Staten Island, where Emil ends up after they arrive, standing guard outside.

After that, things go well until the morning. Danielle mentioned that she has a jealous and unmanageable sister named Dominique (also played by Kidder), and that day is their birthday. Philip decides to add to the festivities with a birthday cake, which gets him murdered for his troubles.

Reporter Grace Collier witnessed the crime, and unfortunately, she can't get the police to believe her. She hires a detective, Joseph Larch (Durning) and they set out to investigate the two sisters, discovering that they were siamese twins recently separated by a doctor...who is Emil!

De Palma was clearly influenced by Alfred Hitchcock, and Sisters was his homage to the latter director's filmmaking, even down to hiring Bernard Herrmann, Hitchcock's preferred composer, to score the film. It's an effective thriller. Recommended movie.