Good

Book 3 of the chilling Darwath Trilogy.

Outside the great stone Keep of Renweth, the night was the
domain of the monstrous Dark — evil creatures that had
erupted from their forgotten lairs for the first time in three
thousand years.
Inside the Keep the survivors of the once-great Realm of
Darwath sheltered, squabbled and fought for power. The
Chancellor Alwir planned to use the wizard Ingold Inglorion
and his disciple Rudy Solis, who with Gil Patterson had
crossed the Void with the wizard from their own world when he sought their help, in a desperate attack on the Nests of the Dark. Bishop Govannin, obsessed by a fanatical fury, sought to destroy magic by murdering the wizards.
No one in that climate of ambition, hatred and fear would
heed Gil's discovery of the truth that lay behind the rising of the Dark — no one except the wizard Ingold.