Ryan Shaw awakens in a strange hospital with no memory of where he is or how he got there. He soon learns that he has survived a fall of seventeen kilometers into the Earth's crust and is trapped underground in the Republic of Inner Earth, founded in 1898 by scientists seeking to create a perfect society and avoid war and unrest. Being the first 'Surfacer' to survive the long plunge into the darkness, Shaw must contend with his newfound celebrity as well as pain and grief at losing his family, friends, and everything he ever knew.

Shaw learns the Republic is embroiled in a civil war with the Tricians, a ruthless faction which has taken control of and enslaved many caverns and cities to form their own nation. With his knowledge from the surface, Shaw joins a team of Republic agents: an escaped Trician slave, a brilliant scientist, a beautiful government agent, and a steam-powered robot, all seeking the means to recreate an artificial star in the underground. Success will mean limitless light and energy for the citizens of the Republic, while failure means oppression and slavery.