Deryni Checkmate (Chronicles of the Deryni)
The late Lester del Rey had a theory about the biological seat of Deryni power, a theory that he could have related in astonishing specificity.  I just remember that he said it must come from somewhere in the nose, something related to the olfactory senses.  I always thought that wa snot a very glamourous way to look at an exciting, epic sweep of fantasy.  But after all, magic has to come from somewhere.--Veronica Chapman, Senior Editor