I was most intrigued by Act Three: The Invisible Girl, a segment that examined the issue of why kidnapping victim Elizabeth Smart was not recognized or detected during the nine months of her captivity in 2002, despite the fact that her captors paraded her around Salt Lake City in broad daylight.
Although the notion was not mentioned on the show, it seems to me that perceptual set may have been behind some of difficulties people had in identifying the girl they saw on the street as Elizabeth, even though some of them actually knew her very well. Her captor, Brian David Mitchell, was a frequently-seen fixture of Salt Lake City and most residents had learned to ignore or pity him and his rantings. When Smart appeared with him, most people ignored her as they had long ignored him OR simply presumed that he had taken a polygamist wife (not culturally unheard of in Salt Lake City).
The fact that many residents saw the young woman and thought, "polygamist wife" and not, "kidnapping victim" may have been the byproduct of their own expections (i.e. perceptual set).
Your thoughts? Check out the show (available as a free podcast) and see if you can generate other explanations for this "hidden in plain view" phenomenon.