Camber the Heretic (Legends of Camber of Culdi, Vol. 3)

King Cinhil, who had assured peace between the Deryni and humans in Gwynedd, was dying. And the regents who were set to rule in the place of his sickly son were evil men who could very well undo all that Cinhil had accomplished. Once they ruled, no Deryni would be safe. The only hope lay in a discovery that blocked off all Deryni talents, enabling them to go underground and appear as humans. But that meant that the race of Deryni could be saved only by being destroyed as Deryni...!