Babylon 5, Invoking Darkness (The Passing of the Techno-Mages Series Book 3) by Jeanne Cavelos

The electrifying space epic reaches an explosive climax when one techno-mage battles the ultimate evil

As billions die and the flames of destruction rage unchecked, the Shadows seem poised for absolute victory. Soon the entire galaxy will fall to their evil. But the war isn't over . . . not yet. At long last, in a forgotten corner of the universe, Galen has finally won the Circle's permission to leave the techno-mage hiding place. He is the only mage who has faced the Shadows and lived, the only one who possesses the unstoppable Spell of Destruction.

Galen's orders are clear. Though the galaxy is being torn apart by bloody conflict–in which his powers might tip the balance–he is to locate only three key enemies and kill them. But Galen has unearthed the Shadows' darkest secret–and discovered a monstrous truth about himself.

In this desperate, apocalyptic battle, there's no telling who will be the victor. Or if there will be any survivors at all . . .

Babylon 5 created by J. Michael Straczynski