Luciferin by J. Peter W.
In the small town of Luciferin, there is no sun. There never has been. And the night skies are filled with thousands of fireflies.
Daniel and his girlfriend have to call off their beach vacation to travel back to Daniel’s home town of Luciferin. The live-in nurse that cares for his elderly parents has disappeared. When they arrive, they find his parents have aged rapidly and seem to have gone mad.
When Daniel spots a teenage girl standing in the yard, he makes the mistake of inviting her in. He quickly realizes the girl’s intentions are far from innocent and calls his sister for help. The siblings wonder if the teenager isn’t involved with the abandoned Lucid Light factory, the children who’ve disappeared, and why all the adults in town look much older than they really are.