This is, I believe, the fifteenth novel in Kurtz' Deryni series. I have read all of them - except the one that directly precedes this one, "In the King's Service." If you must read this book, I highly recommend reading it first. However, I don't particularly recommend reading either of them. This book barely qualifies as a novel. Reading it is akin to spending time with an extremely gossipy acquaintance who insists on chattering at length about people that you barely remember. "Oh did you hear that so & so had a baby? Really, and so & so is marrying so & so, and OH, did I tell you that so & so's son died? Oh, so tragic! I could hardly believe it."
For the first 2/3rds of the book, absolutely nothing happens except history-style updates on characters who are never fleshed out. I'm assuming that I was supposed to have learned who all these people were in the previous book, and that I wouldn't need more characterization after that.
In the final third of the book, a plot finally comes together - people are out to get the young Alaric Morgan, whose parents swore him to the magical service and protection of his king. Things go rather badly, people die. That's about it.