Wars of Light and Shadow #1: The Curse of the Mistwraith book by Janny Wurts

The world of Athera lives in eternal fog, its skies obscured by the malevolent Mistwraith. Only the combined powers of two half-brothers can challenge the Mistwraith’s stranglehold: Arithon, Master of Shadow and Lysaer, Lord of Light.

Arithon and Lysaer will find that they are inescapably bound inside a pattern of events dictated by their own deepest convictions. Yet there is more at stake than one battle with the Mistwraith – as the sorcerers of the Fellowship of Seven know well. For between them the half-brothers hold the balance of the world, its harmony and its future, in their hands.