My wife loves the TV show Ghost Hunters - she's always loved stories about the supernatural, and peoples' pursuit of it, and answers to life after death (now that she's Christian, like me, we have those answers, but the shows remain interesting and that's not necessarily on-topic anyhow). It occurred to me that the only way she might play roleplaying games with me (she doesn't really enjoy the concepts of D&D or RPGs in general) is if I develop a campaign specifically focusing on ghost hunting - which I have plans to do. I'm not sure what system I'll use yet, since I want to use something rules lite so it's easier for her to learn (Do I need a Modern OSR-related hack, or do I go with a different system built for horror games or use... shudder... slimmed-down GURPS? Perhaps CoC will serve me best, now that I think about it.).
Anyhow, I would begin the campaign much as the TV show, with one investigation after another, which progressively get more obviously supernatural. Eventually, after all this leads to success in the characters' lives, the government takes notice, or perhaps a large corporation, and begins to investigate them and what they do. This in turn will lead to ever-scarier investigations, and perhaps put them in the middle of some shady business deals or even a warzone or two if the government is involved. And perhaps those employers want to enlist the aid of the supernatural for their own ends? The possibilities are endless!
PS - The Campaign Notebook series of posts are a way for me to keep track of my inspiration for campaigns so I can get the ideas out of my head, on "paper," and under control. The side effect is you get to see what some of my possible future campaigns will be!