Maker's Curse: Book 4 of Millennium's Rule
Rielle is the Maker, restorer of worlds. She has lost count of the number of worlds she has been sent to save.
Tyen has cast off his old identity. No longer a spy, he now attempts to teach new sorcerers and find ways to counteract the war machines that are spreading throughout the worlds.
But when an old enemy brings news of a dark threat - something far worse than magically dead worlds and dangerous sorcerers - Rielle and Tyen must reunite if they are to have any chance of saving humanity.