The Oak Above the Kings A Book of the Keltiad
On the planet Keltia, Arthur, the lawful heir, leads an army of insurgents against the tyrannical rule of Archdruid Edeyrn. The tyranny defeated, Arthur takes off on a punitive expedition against the planets which supported Edeyrn and returns home to marry Gweniver for reasons of state. By the author of The Hawk's Grey Feather.