Magic Shifts (Hardcover) by Ilona Andrews

Magic is coming and going in waves in post-Shift Atlanta—and each crest leaves danger in its wake in this gripping novel in the #1 New York Times bestselling Kate Daniels series.
 
After breaking from life with the Pack, mercenary Kate Daniels and her mate—former Beast Lord Curran Lennart—are adjusting to a very different pace. While they’re thrilled to escape all the infighting, Kate and Curran know that separating from the Pack completely is a process that will take time.
 
But when they learn that their friend Eduardo has gone missing, Kate and Curran shift their focus to investigate his disappearance. As they dig further into the merc’s business, they discover that the Mercenary Guild has gone to hell and that Eduardo’s recent assignments are connected in the most sinister way…
 
An ancient enemy has arisen, and Kate and Curran are the only ones who can stop it—before it takes their city apart piece by piece.