In the "Gear City", a gear city where machinery and the supernatural are intertwined, Chen Yan, a watchmaker suffering from persecution paranoia, accidentally opened the time corridor in the ancient clock tower and obtained a pocket watch that could see the cracks in time. He saw a doomsday vision in which the "Steam Heart" underground in the city was about to shut down, but found that he had the same appearance as the young man in the photo a hundred years ago. In order to prevent the "dead fog" that comes every 49 years, he teamed up with Su Ling, a knowledgeable archives administrator, to get rid of the cocoon amidst the obstruction of the Exorcist Guild and the strange awakening of the Gear Puppet Worker. Eventually, they touch upon the city's bloodiest secret: the so-called heart, the tormented soul of a dedicated man imprisoned for eternity. Chen Yan must face his forgotten past and make a choice - whether to continue the prosperity built on the eternal pain of his loved ones, or to break the reincarnation and find an unknown but free way for the city to survive.
