This is the third book in the Chalion universe. The story stands alone, but it might be slightly easier to understand the world if one read The Curse of Chalion and Paladin of Souls first. Bujold's Quintarian religion is central to the story, but it isn't explained in tremendous detail in this book. Besides, The Curse of Chalion, where the religion is introduced, is absolutely not to be missed.
This is a tale of romance, mystery, intrigue, and royal succession, suffused with magic related to the religion Bujold created in The Curse of Chalion. It's got a good plot, adventure, excitement, and love, and interesting, non-trivial characters populating a rich and wonderful world. What really makes this book, this series, interesting is the religion at its heart. Bujold postulates a world with real gods, gods who are worth worshipping but whose powers are quite limited, and a church and theology that accept these realities and make a religion that makes sense. And it all gets tied up in an ending that completes the adventure, leaving the main characters with some significant but not-too-immediate challenges, hope of a positive resolution of those challenges, and the immediate prospects of some well earned peace and quiet.
A satisfying story in a remarkable world I'm delighted to return to. 10 out of 10.