Prince of Lies. The Avatar Series

The gods may have been restored to their rightful seats of power-but the end of the Time of Troubles does not mark the end of all strife Although the gods have regained their powers and no longer walk in the mortal world, there is still little peace between them. When their deeply engrained power struggles erupt once more, ex-comrades Mystra-formerly known as Midnight and recently elevated to godhood-and Cyric are bound together in conflict. Cyric, now the god of strife, murder, and the dead, has become even more obsessed with power and revenge.
No longer content with just the Tablets of Fate, he wants the Forgotten Realms all to himself-and to rule them in the name of evil. Only Mystra, the new goddess of magic, has the ability to defeat him and restore the balance that has been lost.