It's not a good sign when you're so bored by the "dramatic" confrontation of two armies midway through a book that you put it down for months and then have to eventually force yourself to finish it.
I had such high hopes for this original Deryni series after enjoying the later prequels back when I was in middle school, but now I'm worried that Tween Alex was just kinda dumb. (Just kidding, he was really smart, and I'm sure Katherine Kurtz improved as a writer as she went along.) But these three books are just so bad. I have a hard time deciding if this one is truly worse than the incoherent mess that is "Deryni Checkmate," but I decided to rate it one star based on the bad taste it left in my mouth as a trilogy-capper, and due to the aforementioned boredom.
There's no way of telling who the main character of this book is. Is it the bold, dashing, nonsensically romance-afflicted, kind of sociopathic half-Deryni warrior Morgan? Is it the waffling, self-doubting half-Deryni priest Duncan, who seems to have more reaction to being asked to hear a confession than he does to witnessing his father's brutal murder? Or is it the Mary Sue cipher of a teen monarch, Kelson? It's hard to say, because exactly none of them enjoy believable character arcs, and none of them are instrumental to the novel's abrupt and deeply unsatisfying climax.
Here are some of the other reasons this book is not good:
The prose is stilted. The magic system makes no sense. The fact that the Catholic Church seemingly exists with no major differences from the real world's version in this fantasy realm is an odd choice, to say the least (but it's central to the series, including the maybe-better books later on, so I'll let it slide). A central conflict between the Deryni and anti-Deryni zealots (the leader of whom can Heal in a rather Deryni-like fashion) is never adequately explained in the first place, then is conveniently resolved in a dumb and morally suspect way. Another, more interesting conflict--the idea that Deryni renegade Wencit of Torenth is so dangerous, and worth opposing, because he does not "suffer" opposing Deryni to live under his rule--is dropped into the story late, in one line of dialogue, and is never referenced again. The social structure and history of the Deryni are underdeveloped and confusing. (Is the Camberian Council unique to Gwynedd? It certainly seems so by the way some members talk to Kelson, but if so, why would the foreign Deryni king Wencit submit to their authority? Are the other members of the Council publicly known figures, like Arilan is, and if so, why does no one register any surprise when their identities are revealed?) Much of the plot hinges on ham-fisted machinations that arise, and are dispatched, entirely offscreen (Wencit's bizarre counterfeit Council, for instance). And so much dialogue is dedicated to recapping, in excruciating detail, events that we just read about, that I wonder if this would even qualify as a novel if all those instances were eliminated.
If you want to dip into Katherine Kurtz, the Chronicles of Camber of Culdi are much better (I think), and these earlier novels are not required to enjoy them.