They're always watching. They're always waiting. They're always starving...

Ten years ago, the sky shattered and the Hellions emerged. No one was able to keep them from destroying the city of Westraven. Now that the bloodthirsty monsters rule the skies and have forced the few remaining humans underground, Claire Abernathy lives in a nightmare. She survives by using her skills as an engineer for a ruthless tyrant connected to her mother and father's past failure.

Then Claire's world is torn apart when her sister Abby is kidnapped by the Hellions, and Claire herself is taken by dangerous sky pirates known as marauders. But Claire will not be intimidated by them while her sister's life hangs by a thread, and so she strikes a deal with them: If they help rescue Abby, she will fix their ship and give them the chance to take the revenge they desperately seek.

As Claire fights for her sister's life, she begins to realize that the Hellions are not the only dangers she'll face. Burdensome secrets and devastating betrayals threaten her at every turn, and if she loses herself to them, it won't just be her life that is destroyed...