Sovereigns - Sovereigns of Bright and Shadow, #3

The barrier has been torn asunder. Now they must find the seat of the Sovereigns' power before the mortal realm and the Between collide, altering the fabric of the know realms forever. Under the Usurper's influence, Leon has left nothing but destruction and undead in his wake. A chilling reminder of the future the world will face if Nea and Garret cannot find the Thrones of Eternity before the Usurper does.
Hunting for clues to the thrones' whereabouts, Nea races to the enchanted isle of Quel'sapar. But with the death ward now linking her keen to Garret's, the itchy stirrings of his corruption could prove a fatal distraction.  The hunt leads them deep into the mountains of the Spine where they will finally face down the Usurper and learn that to liberate the Sovereigns, one of them will have to sacrifice everything.