Ignited Souls - The Guardians of Altana, #2

The demon knows more than he should. Her men gone, allies scattered, and imprisoned within the ruins of Waetherea's palace, elven princess Ara Zypherus stands alone. As Ara's sanity unravels beneath the vile ministrations of the god of chaos's champion- hope is nearly lost. That is, until Raethin Corvus gasps back to life. He's bargained his soul to fulfill his oath of protection to Ara at any cost.
But the clock is ticking. Raethin, along with the Rakevan guardian, and a strange new ally- an elven priestess, race to find Ara, knowing that if princess Ara falls, the Void King will succeed in consuming all life.