Black Earth: Dark Masquerade - The Black Earth Series, #3

Darkness has engulfed the world, and the nightmare has begun. Two weeks have passed since Nathan Pierce battled the Great Witch, Evanescence, and rescued Pearl from her mother's corrupt influence. Nathan now finds himself inhabiting a mall in northern California with members of Absolute's Rebellion, holding onto hope that his sister, Daisy, hasn't been executed for treason yet and keeping a watchful eye on Pearl-an immortal girl branded with a black key mark that could unlock destruction upon the earth.
When a stranger strolls in from the darkness with a lead on Daisy's whereabouts, Nathan sets off on a journey into the Broken Lands to find her. But to save his doomed sibling, Nathan must maneuver through a horrifying landscape of terrifying creatures and violence, dodging both the President of the United States and Legion-an alien entity intent on destroying the world.