4Rook and Gage live worlds apart -- but somehow they must find a way to help one another survive.

Trapped in a life she didn't choose, Rook struggles to find meaning in her appointed role as an apprentice Keeper of ArHK. Even though her mam soothes her with legends of the Outside and her da assures her there are many interesting facts to discover in the Archives, Rook sees only endless years of tracking useless information. Then one day Rook discovers historic footage of the Chosen Ones arriving in ArHK, and she begins to realize her mam's legends are more than bedtime stories. That's when Rook begins her perilous and heartbreaking search for the limitless sky.

Gage is also trapped. Living on the frontier line with his family, his is a life of endless moving and constant danger. As he works with the other scouts, Gage searches for the Ship of Knowledge to help his society regain the wonders of the long distant past, when machines transported people across the land, illnesses could be cured, and human structures rose high into the sky.

Will Rook and Gage escape the traps and perils that await them in order to save each other's worlds? If they don't, it could very well mean the end of humanity.