Sikong Zhen discovers the mechanical beasts in the underground city and studies them privately. Wu Zetian notices something amiss and sends Shangguan Wan'er to investigate secretly, while the Yaotian organization also has its own plans… Several forces intertwine, creating a turbulent undercurrent. Faced with the eventual outbreak of a common crisis, everyone, for the safety of Chang'an, overcomes all difficulties and works together to defeat the mechanical monsters, restoring peace to Chang'an.