Light

Every person has a light behind their eyes. It could be bright or dim, so low it is barely there, but it exists in everyone. It is the thing that makes each person who they are, makes them special, and, sometimes, gives them extraordinary powers, or "light gifts." The Light is what makes everyone themselves, and without it, the Society would crumble.
Until the Dark sweeps in.
No one's Light is safe.
And Cora La Rue is about to find out what a real monster is: one without a Light inside to hold them back from the dark inside all of us.
Switching between Cora's wandering journey across a post-apocalyptic landscape where anyone could be a killer, and the almost equally horrific Society that landscape was before, Cora's accidental quest to bring back the Lights of her people and stop the deadly Dark- whatever it is- could end either in victory for the Society, or for the Dark.
Neither is good.