In the mechanical city "Assel" shrouded in thick smoke and steam, the upper-class nobles monopolize the energy and the sky, while the lower-class rat people can only survive in abandoned mineral veins. Cole, a sixteen-year-old scavenger, accidentally dug up a beating mechanical heart during an illegal excavation. This is not a dead antique, but a fire left behind by the old gods. The Heretic Tribunal in the upper city heard the news and cast a dragnet. In order to survive and unlock the secret behind his heart that is related to the survival of the entire city, Cole is forced to embark on a road of escape and is involved in a bloody storm that can subvert class and belief.
