Archangel’s Prophecy by Nalini Singh

Midnight and dawn, Elena’s wings are unique among angelkind—and now they are failing. The first mortal to be turned into an immortal in angelic memory, she’s regressing. Becoming more and more human. Easier to hurt. Easier to kill.
Elena and Raphael must unearth the reason for the regression before Elena falls out of the sky. Yet even as they fight a furious battle for Elena’s very survival, violent forces are gathering across the world. In China, the Archangel Favashi is showing the first signs of madness. In New York, a mysterious sinkhole filled with lava swallows a man whole. In Africa, torrential monsoon rains flood rolling deserts. And in Elena’s mind whispers a haunting voice that isn’t her own.

This time, survival may not be possible…not even for the consort of an archangel.