Scooby Doo, Where Are You?
It's important to remember that Secret Histories need not be limited to, well, actual history. You can get a lot of dramatic mileage out of taking any story that everyone thinks they know and then putting a new spin on it -- or, in this case, just spinning it a little faster or a little harder in a direction it was already going. We've already demonstrated that we're not too shy about ripping off pop culture for more easily grasped character- and game-hooks; and something like Scooby Doois really only a few steps away from traditional teen slasher horror as it is.
The Framework
As a result, when I was looking for a few familiar faces for a horror adventure, I went back to my childhood, and picked a few old friends to torture. My preferred system for horror (or at least high tension) is the incomparable Dread, in which characters are based entirely on questionnaires supplied by the GM and then filled out by the players. The ability to control the questions gave me a great way to shape the direction of what is a de facto Secret History of Mystery Incorporated, but it gave the individual players maximum power to shape the details.
The nice thing about using such familiar characters is that you can run them through a thin pastiche of essentially any "meddling kids" scenario, albeit in this construct with a few more adult themes (and an intentionally absurd guest star). Since we here at the Illuminerdy live to serve, we thought we'd make it easy for you, and provide the questionnaires for your own nefarious uses.
And we would have gotten away with it, too...