not so much a story idea...more of an idea for an epilogue twist that can be added to most any serious story.
By serious story, I mean an actual novel type, full length story with plot beyond just sex scenes.
The story I envisioned when I had this idea was a kind of fantasy story where an amnesiac man wakes up to discover himself in a fantasy realm. He travels around while trying to recover his memory and has lots of adventures/interactions with the inhabitants of this fantasy realm. Eventually he discovers a ring that will return its owner to their proper place in time/space. As it is rather obvious he didn't come from this world and he still hadn't recovered his memory, he puts on the ring in the hopes that it will work and transport him back to his world in a time/place that would allow him to recover his memory. As he puts on the ring, he disappears in a flash. Story ends.
Epilogue has a woman putting down the final paper of a thick stack. She then turns to a man sitting near her and asks where the rest of the story was? He responds that is the end. She exclaims what?! what about his memory? does he ever get it back? where did he come from? did the ring actually work? are you saving those answers for a sequel or something?
He grins and responds no.. no sequel, and no answers. he then leans forward, placing his arms on his legs as he starts to fidget with the small ring he always wore on his pinky finger. In fact, I dont think I am even going to publish this one...its too personal. end of epilogue
The twist is that the primary story is written as a fantasy or fiction novel.. just something that obviously can't be real in our world. Then in the epilogue, reveal it as a manuscript being read by someone in our world...but give some hint that it might actual be real (the small ring on his pinky and his comment that it was too personal). Such a twist could be adapted to many stories in many different ways. Another way is it being a bedtime story being told to a child but as the parent leaves the room after getting the child settled for the night, he rubs the ring as he sighs in remembrance. Etc.