It started with the insects.The mass die-offs had been a warning unheeded. Before society realized the danger, the Earth had inexorably begun a transformation into a place where life could not survive. A small group found shelter in the Arc, an underground refuge safe from the toxins ravaging the surface.After centuries of darkness, humanity's second chance is running out-and Raven Wilder knows it.Her job fixing the machinery in the Arc makes her aware of how close everything is to breaking down. When the systems fail, the last survivors of the human race will suffocate in the tunnels meant to protect them from the deadly air outside-starting with the most vulnerable. Unfortunately, in an example of history repeating itself, those in charge dismiss her concerns.When her six-year-old begins showing signs of oxygen deprivation, Raven refuses to go quietly into oblivion.She will break every rule to keep her daughter alive.