Up Jim River is the sequel to Flynn's earlier work,
The January Dancer, a book that I haven't read. Not having read the first book did not detract from reading this one; while there were references to the Dancer, they were like any background stories of books. There was one thing about this being a sequel: after finishing Up Jim River, I now want to read The January Dancer.
Bridget ban has disappeared. As she was one of the League's elite agents known as the Hounds, this is not normal. Then even her fellow Hounds cannot find her, and it falls to Mearana, her daughter and a Harper, to find her. She enlists Donnovan, an old acquaintance of Bridget ban's and once agent of the Confederacy. But the leaders of the Confederacy have either punished Donnovan or performed a failed experiment on him: there are seven personalities within him, and they frequently have conversations and arguments with each other. So they go out looking throughout the perrifery of civilized space for the Hound, or for what killed her.
This is a good book, and Flynn has a good grasp of a certain complexity that I have not often seen in many sci fi books. The League is a collection of different governments on many planets. Most sci fi writers who take this situation will talk about the government of Planet X, or the King of Planet Y. Flynn, however, has his planets having multiple governments, like Earth is. It adds a certain versimilitude to the writing which I find refreshing.
As a final note, the ending does ensure that there will be another book about this universe.