The Ring of Allaire Winter King's War #1 Susan Dexter Del Rey Fantasy 1982
Master magician Blais was dead, murdered by the evil ice-lord Nimir.
Now there was only Tristan, an ill-trained apprentice, to carry on the quest to rescue Allaire, a princess held in enchanted sleep in Nimir's frozen halls.
Though a thousand master mages had already failed in the quest, Tristan must succeed or all of Calandra would be doomed by Nimir's greed. First Tristan would have to find the wonder-horse Valadan, who had vanished long ago.
Then he had to secure the aid of the one knight among many who was a true Heir to the Throne. Together, they must overcome the Guardian dragon of Nimir's realm. After that well, there was still the tenth ring to be found, since Allaire was powerless without it.
Nothing, of course, was ever that simple. There were complications . . .