Spacer and Rat is a young adult science fiction novel by Margaret Bechard. It is an intentional throwback to the golden age of science fiction, an adventure story in a future based on a linear extrapolation of technological development and the assumption that space travel will be cheap. No aliens, though.
The story is set 100+ years in the future, on a large station in the asteroid belt. This is only one of many stations, the asteroid belt being one of the hottest pieces of real estate in the solar system at the moment. Earth is having yet another epidemic, and the refugees are flooding in. The descendants of the original settlers (the Spacers) are less than thrilled about this, but it's good for business. Mostly. Occasionally you get a kid who is orphaned or abandoned in the mass migrations, and they become a drain on society. The breath valuable oxygen, they steal food, and then they try to fight back when you finally catch them and turn them into the company police. These are the Rats.
This is the story of a younger Spacer, Jack, who discovers a Rat, Kit, with a dangerous secret. Kit is an exceptionally good Rat, and manages to survive on the run perfectly well, but as it becomes more and more apparent that her secret is of interest to just about every powerful faction in the solar system, it becomes clear that she can't make it on her own. Jack slowly comes to the realization that Rats are human too, and that he might actually want to help her. The majority of the story involves a paranoia-inducing series of close-calls, coincidences, and disasters as an ever-increasing cast of characters try to catch the Rat. The author also spends a lot of time developing the world (which is pretty cool), and a little bit of time developing the characters (who are supposed to represent average teenagers). Overall it's a pretty good book, but it is not likely to become even a niche classic.
One of the hooks of the book is that it is packed full of references to classic SF books and authors. These tend to be obvious and bland, but it is still somewhat amusing. I have the impression that this is intended to be a Heinlein-type story, but it generally fails to capture the best aspects of Heinlein's stories -- the political and social messages are lacking, the characters are not as strong, and the science is comparatively weak. However, as a contemporary story for a young adult who is just discovering SF, this is an interesting example of accessible 'classic-type' SF. Despite what you may remember, classic SF was often not very good. It earned its points on being interesting, and interesting is a moving target, so updating the genre with some trendy characters is not a bad thing. I found it refreshing to read some YA SF that didn't involve transhumanism, a repressive dystopia, or alien encounters as its main theme. On the other hand, fancy technology may not be enough to carry a book any more, and there isn't anything that is new and exciting in Spacer and Rat. Except perhaps to young readers.