What could be a better prompt of fiction than the tension of a secret?
There are compilations of secrets, such as PostSecret: Extraordinary Confessions from Ordinary Lives and its two (so far) sequels. They come from a project whereby people write their secrets on homemade postcards and anonymously mail them in.
But even more accessible are the secrets posted on the project’s website. They simply beg for a backstory and a what-happens-next.