Gereient is the humble but magically gifted farmboy. Averil is the astoundingly beautiful but kind and humble lady, raised by nuns because her father couldn't bear to look at the reminder of his late wife. They each belong to allied noble orders (the Knights of the Rose and the Ladies of the Isle), and eventually they will meet and fall in love. Their love will undoubtedly be tested by the difference in their social stations and the Darkness Sweeping the Land. I don't know, however, because I gave up on this book about halfway through. This book is what you get when the Belgariad and Arthurian myth are thrown into a blender, and then only the murkiest dregs are printed. It's a terribly boring mishmash of Christianity-as-last-hope-against-the-Serpent and farmboy-loves-princess. People are perpetually telling the farmboy how humble and gifted he is. Averil is continually far too mature and skilled to be 15. And the villain gets a chapter or two to explain his Evil Plans and how Evil is all he desires and so on and so forth every time the reader is getting truly bored with the farmboy and the lady's meet-cute. There is absolutely no narrative tension, the characters are cardboard cliches, and the entire thing is one huge Fantasy Trope enacted in McEurope. It is not, however, actively horrifying or insulting, so I suppose that's something.
Kathleen Bryan is actually the pseudonym of Judith Tarr, which explains a great deal.