After the Posleen War ends, a small band of Posleen is smuggled off Earth in secret to start their civilization anew. They start on a sort of quest to find a home. At the same time, elements of humanity led by the Catholic Church aim to bring religion to these Posleen, saving their souls and making allies of them.
If you liked the other Posleen books, you will probably enjoy read this one. It doesn’t have much value if you haven’t read them, especially Yellow Eyes. It is reasonably good fun but there are no massive stakes. In some ways it is a setup for the Hedren War. The discussions on the role of religion are reasonably interesting, and superficially contrarian for a science fiction book.