@foxybilly I don't actually have strangerville, so I'm probably not the best person to answer this, but would it be possible to start a new save, solve the mystery, and then use the "save as" button in the Sims 4 menu to save a "starter save"?
That way, anytime you wanted to start a new save, just load that starter save, and do another "save as" under a different name, and the mystery will already be solved?
(Probably best to turn off aging and neighborhood stories while you solve the mystery. That way, all the premade sims stay the same age and won't die while you're playing through it.)
I hope this makes sense. It's kind of hard to explain how to do it without being able to show you. I'd be happy to answer any more questions if needed.