Here’s another idea for a plot which would work great for both fiction and RPG sessions.
Michael Persinger, a Neuroscientist, investigated a case in which a teenager reported that she received nocturnal visits from ghosts. The scientists were called in at the request of the mother, and determined that a clock close to the girl’s head combined with a mild brain injury she had received as a baby caused the hallucinations. The clocks was removed, and the “visitations” stopped.
The article in the Scientific American goes into greater detail, especially on follow-up experiments designed to determine scientific causes for sightings of the “supernatural”, including experiments to test whether a person who wants to see a ghost is more susceptible to such causes and thus more likely to “see” a ghost.
This would work well in a setting in two ways; you can either take the “ghost baby” story and turn it into an investigation (and, since an electric clock is probably very anticlimactic, you may wish to use the devil / evil spirits / space aliens as the cause), or you could take the scientific experiments in general to kick-start a campaign. The investigators either come to delve into the “true supernatural” (Ghostbusters did it, why not you?) as a consequence of their inquiries or they uncover pranksters or frauds who may even be making a great deal of money off of the unsuspecting. The later works especially well if your players actually do expect ghosts.