The Unexpecteds. The Smolder, #3

During the reign of Greenley the Third, eleven-year-old Shayna Miller is living underground with her adoptive parents, hiding from the government, which is trying to perfect society by killing anyone who doesn't meet their biological and psychological standards. The experiment has been going on for generations, and so an extensive parallel society of freedom lovers has developed. They call their society Subterra, because so many of them live underground, in tunnels and caves.
They refer to their period of history as The Smolder, while adopting a motto of 'Down, but not out.' In Shayna's time, the younger generations, who have never known what it's like to live openly above ground, are getting restless, and wondering if it might be better to risk their lives in a revolt, rather than live in relative safety, but in cramped conditions, with limited options. Still, for the most part, most Subterrans have settled into what has come to seem like a normal life to them, simply staying unnoticed as much as possible, and contenting themselves with making the best of life in whatever little community they're in.
But Shayna's father keeps moving her family from place to place inside Subterra, almost as if he's trying to run from something inside Subterra itself. But what?