It takes a book like this to show you how full and rich the Star Trek universe has become. The story is clearly set in the DS9 milieu, ranging from Bajor to DS9, Earth and Cardassia, but it really could have been told anywhere. However, what the Star Trek backstory brings to the overall tale provides such a layer of richness to it, that you're left with a memory of how good the world is.
The story centers around a young Cardassian, who was orphaned on Bajor, and raised by Bajorans as one of their own. When he travells to Deep Space Nine, and his true identity is discovered, Sisco feels he has no choice but to uproot him from his current life, and change the boy's future forever.
For his part, the young man doesn't go away willingly, but he feels he has little choice. His new family is cordial enough, and they bring a certain history and opportunity that he finds difficult to turn away from. He spends the next few decades planning to find his way back to his family on Bajor, but things keep getting in the way. Eventually, the young man finds a cause to believe in, and follows it with all his heart, and even most of his life.
This is a story about changes, and how we all have to adapt, some times several times to radical changes in our lives. For most of us, what we do along the way is what matters.
I'm sure there are going to be complaints that this wasn't really a Star Trek book. While the story existed in the universe, and followed the timeline of Cardassia's history pretty solidly, it really could have been told anywhere. I agree, the story could have happened anywhere, and could even have been set in modern day. But it truly is the layers of understanding and complexity that the Star Trek history brings that makes this book something special. I don't truly recommend this book for fans of traditional, monster-of-the-week type Star Trek stories. But for those of us for whom DS9 was the best of the series, this book will be satisfying and enjoyable, and remind you how good it was.