In the giant floating city "Baiyujing" made of steam and gears, logic and machinery are the only yardsticks for measuring everything. Here, sophisticated clockwork dolls are loyal servants, huge brass airships streak through the leaden sky, and the heart of the city is driven by a super differential engine called "Tianshu". However, when a series of bizarre murders occurred one after another that could not be solved using mechanical principles, the foundation of this rational city began to shake. Ancient runes appeared on the body of the deceased, and no trace of any crime tools could be found at the scene, as if something invisible was harvesting life.
When the ultimate in rationality meets an unspeakable mystery, Gu Xuanji has no choice but to join forces with Zhu You, the "magic stick" he despises most. One of them holds a sophisticated detection instrument, and the other relies on a compass and talismans to shuttle between Bai Yujing's glamorous upper class society and the rusty lower-class labyrinth. What they want to investigate is not only bizarre murders, but also the taboo truth about "gods" and "machines" that was deliberately buried when this giant floating city was first established.
