It's the story of a Chicago area nanny, Vivian Maier, who carried a camera with her and did street photography for decades. She never showed her work to anyone and John bought a case of the negatives on auction from a company that rents storage lockers.
It turns out she was pretty good and produced a huge volume of work that no-one has seen.
You can see a short video on Chicago Tonight.
Or go to the website and see some prints. John has spent hours/days trying to find out more about Vivian, and scanning her negatives. You can help out with the documentary here.