It's been five years since the Pulse, the mysterious event that led to the complete failure of the world's electrical grid and plunged society into permanent darkness.

Nurse Lucy Goodwin, her brother Jack, and her young ward Norah now live in Promise, a small community that formed in the wake of the technological apocalypse. Their lives are not easy, but they have food, water, weapons, and medical care. They are among the lucky ones in a world beset by lawlessness and starvation.

But after encountering a trio of mysterious bandits, Lucy and Jack learn that a new threat lurks on the horizon, one that could spell the end of their community ... and their lives.