Orlo the deliverer has spent his entire life living in the Conclusus-an underground world where lush gardens grow on top of magnificent towers and a steam filled air balloon is the preferred method of travel by the higher class. On an unplanned trip to the Hall of Healers, Orlo overhears news of a tournament and sees the opportunity to not only increase his social status but fulfill his heart's desire-to be an inventor. When he is ordered to retrieve a mysterious package from the Liberum, a vile place where the steam that powers and lights the Conclusus is processed by lawbreakers, Orlo's dreams of inventing will be altered and his relationships questioned as an unexpected enemy emerges and reveals the truth behind the life he has always known.