I agree with Tardis (below). This is the fourth book of a series. Unlike authors of some series, Bujold does not prep you much with what has already gone on before in the story. This is not a negative in my mind. The whole series is well-worth reading. I got thoroughly hooked after book #1. book #2 was very good, book #3 OK, and this book, #4, very good.
Bujold, in this series explores the various aspects of prejudice and set beliefs. She does it with a great set of characters, an imaginative saga of daring deeds and romance, with some truly awesome monsters thrown in for good measure.