The Lost Mage (The Age of Oracles #2)

The oracles have always been the guardians of peace. Now they are the heralds of war. After a century of planning, their strike is swift and brutal. In a night of upheaval the kings and queens are cast from their thrones, their kingdoms replaced by a Mage Empire. The people are quick to resist but freedom lies in the hands of an outcast.
Hunted by soldiers and assassins, Raiden retreats to a final refuge. As he prepares his last stand an unexpected ally arrives at his door. She may be poisoned, but she is far from powerless. Together they will build a rebellion that will defy the Empire. As the world prepares for a mage war, one oracle is noticeably absent, and rumors abound as to her fate.
Betrayed by her oracle sisters, trapped in an anti-magic sphere, Alydian rots in solitude. Each day she fights despair and madness, and plots her escape. With her magic bound, even she believes she is helpless. But such power cannot be shackled. When it is unleashed Alydian will break mountains.
And the oracles that betrayed her.