I think I read this no later than the year 1986. English language, hardback, available in a public library in Indiana in the mid-1980s. I don't think it was by any of the Big Names of 20th Century science fiction, or else I would have run across it again by now. It was a stand-alone novel; no cliffhanger ending, and no indication it was intended as part of a series.
The novel is written in the third person, with the emphasis on the thoughts and actions of the male protagonist. I think his thoughts were the only ones we saw throughout the entire book, but I could be forgetting something. Here's what I remember about the plot.
As the novel starts, we are seeing Protagonist (as I call him) arriving by spaceship to begin his prison sentence -- which I believe is meant to be the rest of his life, however many years that may be. I don't recall him thinking anything along the lines of "if I just keep my nose clean for the next ten years, I can get parole!" I can't remember what Protagonist was supposed to have done. I seem to recall that this prison planet is a future version of Earth. If I'm right, then the planet is no longer densely populated with billions of people cluttering the place up. More of a sparsely populated "wild frontier" area. But I don't recall what reasons were given for the fact that the prisoners were basically the only people in sight, such as a nuclear war a few centuries earlier, or some other catastrophe.
Most of the novel is set near where Protagonist is dropped off. I think it may have been stated or implied that the area where the ship landed was the only functioning spaceport on the entire planet. I think the spaceport and the nearby town are in the foothills near the base of a mountain range (and I keep thinking of Colorado in particular, but that may just be because my family moved to the Denver area not long after I read this book). I think a lot of the local prisoners work at some sort of mining activity in the neighborhood -- although I'm pretty sure that they are not "prisoners" in the sense of being locked up in cells every night; just in the sense of being stuck on Earth and not allowed to leave. I don't clearly remember this, but I suspect that there was some economic incentive, such as: "We will trade you consumer luxuries from offworld in exchange for how much of Substance X" -- meaning whatever the heck they were mining -- "you have to offer when we make our monthly visits in a starship." (I don't swear the visits happened each month; that's just an example.)
Soon after arriving, Protagonist meets a girl. I am almost certain that she is no more than 14 years old -- not prepubescent, but younger than a leading man's girlfriend/love interest/etc. would normally be in modern literature. (No, they don't end up sleeping together.) She seems to be going out of her way to get his attention -- she is intelligent, headstrong, aggressive in the way she speaks to him, and I think she comes across as a something of a smug know-it-all. (Granted, if she's been here for years, whereas Protagonist has just arrived, then she has considerable justification for feeling that she knows a great deal more about local conditions than he does.) I don't remember if the girl is stated to have been born on the prison planet, or if she was brought here with her parents, or what. (I strongly suspect that she had not committed some terrible crime at, let's say, the age of 10 or 11, and been sentenced to spend the rest of her life on Earth as punishment for her own sins. I don't remember getting a "hardened criminal" vibe from her, but these memories are at least a third of a century old.)
At some point, it is hinted and then stated that the girl has some unusual ability. I'm thinking something "psychic," but not necessarily being able to telepathically peek into protagonist's mind and know exactly what he is thinking.
It also becomes clear, somewhere along the line (not in the first few chapters, I'm pretty sure), that Protagonist has a hidden agenda. Perhaps his conviction of a major felony was a fraud, and he's actually the future equivalent of "an FBI agent going deep undercover." Perhaps he really did do whatever he was accused of, but he wanted to get caught and convicted as part of a deeper plan. (Similar to the starting premise of the much later TV series Prison Break, but that's just a guess.) Perhaps someone has offered a convicted man "a deal you can't refuse." But at any rate, he's not just another thug hoping to find a way to "settle in for the long haul" as part of the local society; as I recall, he hopes to someday get off Earth and be a free man again, if he plays his cards right. Protagonist appears to be sneaky, determined, an excellent fighter, and so forth. (Sort of like what you'd expect from a military commando type, although I don't remember if he had any formal military training from his pre-prisoner days.)
Protagonist comes to realize that a big shot in the prison colony has some sort of secret deal going on. I think with some non-government faction that has its own starship for making covert visits to the prison planet as part of some high-stakes plan. Somehow, Protagonist (probably with the help of the girl) foils their diabolical scheme -- whatever it was.
The story was written in the fast-paced style of an adventure novel. We didn't have anyone holding up the plot for several pages at a time to give lengthy lectures on sociopolitical theory or economic strategy or anything similar; we followed a "lone wolf" from one interesting scene to another. I think this book was pretty short; i.e. not much more than 200 pages (or maybe even less).
In the last few pages, there's a scene where Protagonist and the girl are having another conversation, and she deliberately says something to tease him, taunt him, or something like that. I don't remember the wording, but it was obviously meant to get under his skin. He suddenly gives in to an impulse and grabs hold of her and pins her down on the ground, and she suddenly seems scared. He may or may not give her one quick kiss before he suddenly lets go of her, backs off, and says dryly: "Try that approach again in another five years, and you might manage to seduce me." I don't remember what she says or does then, but the implication is that him grabbing hold of her for a moment is, in fact, something she was kinda hoping he would do; since she doesn't say a thing to contradict him on that point. (I think she may even laugh at the realization that he had seen right through her.)
My impression is that Protagonist is about to leave Earth on a ship during the scene I mentioned in the previous paragraph -- he is in a very good mood because, somehow, he has "earned a pardon" or "is being brought in for debriefing" or "has gained access to a starship" or in some other way is heading offworld for a while. I don't remember if the girl is staying behind by choice, or if she'll be sent off to a nice school for a few years, or what. But his remark about "seducing me" indicates at least the possibility of a romantic happy ending for both of them at some future time.
So! Does anyone think all this sounds familiar? I'd like to refresh my memory of it and see what I think of the writing style after all these years.
P.S. To save you some time, here are a few "prison planet" or "prison colony" stories which this book definitely was not. (Although I read most of them around the mid-to-late 1980s.)
"Coventry," by Robert A. Heinlein.
The Status Civilization, by Robert Sheckley.
Police Your Planet, by Lester Del Rey.
The Escape Orbit, by James White.
The Beyond, by Jean and Jeff Sutton.
Escape Velocity, by Christopher Stasheff.
The Four Lords of the Diamond series by Jack L. Chalker. (Four novels; each set on a different prison planet within the same solar system. Answering a recent question about that series was what reminded me of this prison planet novel which I'd never managed to track down.)