While sorting through her grandfather’s old house, Zhang Lin, a PhD in theoretical physics, is unexpectedly transmigrated to Chang’an during the Tang dynasty by a bloodstained jade pendant. There he meets Li Ruoxin, the legitimate daughter of the Duke of Qingguo, who looks just like his deceased beloved, Wang Yutong. Through a series of mishaps, he ends up taking shelter in the duke’s residence as a servant.
Using modern knowledge, he improves food carriers and repairs waterwheels, helping the duke’s household resolve a crisis in grain transport. But Han Yingjie, heir to the Duke of Rongguo, steals the credit, and Li Ruoxin clearly rejects his feelings. Later, when stolen blueprints make the duke suspect and imprison him, the jade pendant stirs as a fire breaks out in the woodshed, helping him return to the modern era.
Back in the present, Zhang Lin discovers that he has gained the ability to control water, but he is declared dead and his old family home is about to be sold off. By chance, he transmigrates to the Tang dynasty again and becomes embroiled in a palace crisis. After he and Li Ruoxin endure life and death together, he awakens the power of chaos. The two travel to Kunlun Ruins to uncover the secrets of the pendant and their own powers. They awaken the will of the light wheel and must choose between staying behind to protect the world or returning to ordinary life. In the end, they decide to take their powers back to Chang’an.
Upon returning to the Tang dynasty, they witness the duke’s household fall. Grief-stricken, they face Li Heng before the Taiji Hall as he tries to seize power through a blood sacrifice. With the light wheel’s power, they kill Li Heng and seal away the lingering spirit of the traitor. Once the crisis is over, the two decline the position of Imperial Preceptor and choose to shoulder the duty of guarding the anchor point between eras and protecting the world.
