Pokey is lost in Cardboardia, and her older brother, Mac, and friends, Maisey and Bird, are desperately trying to find her. Taken in by a band of wild witch girls--friends or foes?--Mac, Maisey, and Bird learn more about how the world off Cardboarida works. What's in all the boxes? What are the rules of travel?

They also learn that there are a few humans in Cardboardia, like an old man named Warwick, who teaches Bird how to manipulate paper pulp who also tells them the rulers of Cardboardia want to end it.

Then a posse is sent for the kids by the Gray King, and a full-on battle ensues: Maisey, Mac, Bird, Warwick, and the witches vs: the Gray King's coal monsters, who threaten to burn down everything. The stakes just got a whole lot higher. . . .