Summers at Castle Auburn is a quiet romantic fantasy that addresses social problems, but keeps it in the background. Our heroine is a young woman named Coriel who spends summers at Castle Auburn, the royal palace. She is the bastard child of the bastard son of noble and is–pretty much without her actual awareness for most of the novel–being groomed for an advantageous or at least politically useful marriage. She has a close relationship with her half-sister, has a crush of her sister’s fiancée, and is somewhat feckless and fancy free. Fortunately, she has a strong vocation for becoming a healer and has no intention of ruining her relationship with her sister by acting on her crush.
The plot follows a “coming of age” trajectory where Corie slowly becomes aware that life at the castle is not nearly as idyllic as she thought it was when she was a child. She also approaches awareness that slavery might be wrong, though she does not quite approach the realization that the magical non-humans being enslaved are people. (This assessment may be a little harsh because Corie goes off on a hunt intended to capture an aforementioned magical non-human and the way it’s framed is slightly disturbing when you realize they’ve gone off to try to capture a person, not an animal.) Another aspect of the coming of age plot involves Corie’s eventual realization that the prince she had a crush on is not a very good person. This leads to her making a fateful decision that results in her being banished from Castle Auburn. (Which at this point she doesn’t care about.)
There is also a side plot involving Corie’s uncle (who is a slaver who specializes in capturing and selling the aforementioned magical nonhumans) marrying the queen of the magical non-humans after kidnapping and selling the queen’s niece. It really isn’t explained very well what the queen hoped to accomplish by doing this, since even if she could get the uncle to agree to stop hunting her kind, this would not be a binding contract to any other slaver. (It also isn’t explained why the marriage was allowed to occur in the first place since the humans were extremely xenophobic and normally kept the non-humans in chains so they couldn’t escape or fully use their powers. It seems more likely they would have done something similar to the queen.)
The ending is a happy one, if somewhat unsatisfying, since it results in Corie’s eventual return to Castle Auburn which is not actually a place she wanted to be anymore. Corie gets an unexpected marriage proposal, her half-sister is able to marry the man she loves, and the magical non-humans are back in their home kingdom and so on. While I liked some of the character interactions and found the world building to be interesting I really disliked the lack of agency possessed by the non-humans who seemed to be there mostly for Corie to come to the realization that both she and her half-sister were also trapped by the expectations of their elders.