The plainclothes cops searching for a serial killer tell the Newton clan that they're census takers looking for a picture of a "normal American family." It's a cover story, but - through Shadow of a Doubt - Hitchcock suggests that an average family might be the perfect place to discover perversity. Within the Newton parlor, we find Mr. Newton (Henry Travers) and his friend (Hume Cronyn) cheerfully obsessed with crime fiction and the details of murder. In the kitchen, attempting to get the "census takers" to capture her cooking prowess, we see Mrs. Newton (Patricia Collinge), a woman who's oddly devoted to her brother and a little absentminded. Walk up the stairs (where horror usually lurks in a Hitchcock film) to the room that Uncle Charlie (Joseph Cotten) is currently borrowing from his niece Charlie (Teresa Wright) and you'll witness a curious relationship.
We're introduced to both Charlies as they're lying in beds, as if they're mirror images of each other. When we see them together in the film's early scenes, Hitchcock frames them almost as lovers. The reading of the two Charlies' relationship as incestuous doesn't require much of a stretch of the imagination. They grow apart because of Uncle Charlie's horrible secret, but there also seems to be a sense of romantic betrayal. Charlie Newton suspects that something's not right when her Uncle regifts a ring (one that we learn belonged to a widow who he killed) to her. Uncle Charlie is suspicious not only of young Charlie's cooperation with the police, but also takes offense at Charlie's flirtation with a young policeman. He chastises the two for being alone together in the garage and then uses the garage in his first attempt on Charlie's life. Slipping these romantic symbols into the thriller amplifies the abnormal nature of this average family.