What Happens in the Darkness by Monica J. O'Rourke
Manhattan died, along with much of the country. Twelve-year-old Janelle lost her family in one horrific night and managed to escape into a no-longer-recognizable city. As she struggles for survival, she comes across something much worse than the decimated landscape, much worse than the enemy soldiers patrolling the streets night and day. Another force has been unleashed, one hell-bent on destroying the invading enemy—but now that they’re out, there’s no turning back.