The unforsaken Hiero

From back cover Del Rey paperback April 1984:

Betrayed!

Per Hiero Desteen was alone, weaponless, and without food or water, facing the unknown perils of the desert in this grim world, five thousand years after the holocaust known as The Death.

Sent south to spy on the evil Brotherhood of the Unclean which fought to destroy the emerging civilization of the north, he had been welcomed as the son-in-law of the King of D'alway. Welcomed, honored -- and betrayed! Now his wife and all he loved were lost. ANd the mental powers which had enabled him to defeat every previous trick of the Unclean had been burned from his mind by drugs.

North, his numbed mind told him! North, where he might find help. But without his lost powers, he could not suspect the command was a subtle, cunning lure. Somewhere ahead, a creature that should not have existed was calling him to a meeting he could not imagine.