Deryni Rising (Chronicles of the Deryni, No 1)

In the kingdom of Gwynedd, the mysterious forces of magic and the superior power of the Church combine to challenge the rule of young Kelson. Now the fate of the Deryni -- a quasi-mortal race of sorcerers -- and, indeed, the fate of all the Eleven Kingdoms, rests on Kelson's ability to quash the rebellion by any means necessary . . . including the proscribed use of magic!