The Invasion (2007) on Netflix

For Dr. Carol Bennell, a psychiatrist, the first sign that something is wrong comes from the patient who has been seeing her for four years. "My husband is not my husband," she says. Carol prescribes an anti-psychotic, but she'll soon learn the woman's statement was perfectly rational. After Carol drops off her son to visit his father, the thought occurs to her: "My ex-husband is not my ex-husband." More and more, those around her are behaving oddly. They're cold, emotionless. Meanwhile, her romance with Ben Driscoll, a research scientist, reaps unexpected benefits. She asks him to examine a weird substance she found in the neighbors' Halloween candy. What looks like a thin slice of flesh proves not to be some prank, but an alien substance that will be the key to learning why everywhere on Earth people are becoming what they are not.