In an alternate Victorian England those who are wicked are marked by the smoke that pours out of their bodies. The aristocracy are clean, proof of their virtue and right to rule, while the lower classes are drenched in sin and soot.

Thomas Argyle is the only son of a wayward aristocrat. Charlie Cooper is his best friend. When Thomas finds himself under the boot heel of a sadistic headboy in the treacherous halls of their elite boarding school, he and Charlie begin to question the rules of their society. Then the boys meet Livia, the daughter of a wealthy and powerful family. She leads them to a secret laboratory where they learn that smoke may not be as it seems, and together they set out to uncover the truth about their world.