Gavin Guille, ex-emperor, ex-Prism, ex-galley slave, formerly the one man who might have averted war, is now lost, broken and trapped in a prison crafted by his own magical genius. But Gavin has no magic at all. Worse, in this prison, he may not be alone. Who will fight to prevent a tainted empire from becoming something even worse? The hugely anticipated fourth novel in the acclaimed Lightbringer series.