Sisters (1973 film)

Sisters also known as Blood Sisters in the United Kingdom is a 1973 American psychological horror film directed by Brian De Palma and starring Margot Kidder, Jennifer Salt and Charles Durning. The plot focuses on a French Canadian model whose separated Siamese twin is suspected of a brutal murder witnessed by a newspaper reporter in Staten Island.

Advertising salesman Philip Woode Lisle Wilson is the victim of a prank on a Candid Camerastyle television show and wins a dinner for two at a New York restaurant. He takes with him Danielle Breton Margot Kidder, a naive young French Canadian model and aspiring actress who was hired as part of the prank. At dinner, they are interrupted by Danielles controlling exhusband Emil William Finley, but Philip has him thrown out by security. They arrive to Danielles Staten Island apartment, but spot Emil waiting outside Philip pretends to leave to lure him away, then returns through the back entrance and the two make love on the living room sofa.The next morning, Danielle wakes and feels unwell. Philip overhears an argument between her and her sister in the bedroom, and accidentally knocks Danielles pills down a drain. Danielle explains to Philip that her twin sister Dominique had arrived to visit because it is their birthday, and also asks him to go to the drug store to pick up some more pills. He does so, and also buys a birthday cake for the two. When he returns, he is suddenly stabbed to death by Dominique, who is crazed and delirious. ........

Source: Wikipedia