Sander Jorve just wants to keep his wife and son safe. Living in the brutalized lower class of Lantern City means living in near constant darkness, the enormous walls of the city always looming overhead, while the upper class enjoys the elevated, interconnected towers and airships above. When Sander's brother-in-law, the persuasive activist Kendal, convinces him to infiltrate the brutal ranks of the Guard, he's set on a dangerous path that will test his abilities and beliefs, all in the name of making a difference for his family and his caste.