Malicious - The Puzzle Box Trilogy, #3

After the events of Malevolent and Malcontent, Libby and Mal are reeling from their soul separation. Libby has learned to use life motes in new, amazing ways. Mal has regained his humanity, yet is crushed under the weight of the devouring power laid upon him. Despite this, their devotion to each other has grown into passionate adoration. When a new type of undead appears, Mal tries to stop the revenant's insane misuse of magic.
The revenant is aided by a terrible monster called the Hunger. Not even the Marchers can stand before them. Now Mal and Libby must discover their own deepest secrets to end the zombie apocalypse and defeat the revenant and the Hunger, or lose everything they hold dear.