While visiting an exhibition of Republican-era artifacts, modern history student Yu Xiaoxuan is drawn to an antique pocket watch. The moment she touches it, she transmigrates to Shanghai in 1935 and finds herself in a completely unfamiliar era.
On the chaotic streets of Shanghai, Xiaoxuan nearly gets hit by a rickshaw, but a young officer passing by, Cheng Yuanzhi, rescues her. Suspicious of this strangely dressed woman whose behavior is completely out of place, Cheng Yuanzhi nevertheless finds himself inexplicably drawn to her.
Xiaoxuan is taken to the police station for questioning. She makes up a story about being an overseas Chinese returning from abroad, but can't explain why she lacks so much basic knowledge. Half convinced, Cheng Yuanzhi bails her out.
With nowhere else to go, Xiaoxuan reluctantly accepts Cheng Yuanzhi's offer to stay at his home for a while. The two begin an unusual life under the same roof. Xiaoxuan is fascinated by Shanghai in this era, while Cheng Yuanzhi becomes increasingly captivated by the mysterious woman.
As they spend time together, Xiaoxuan inadvertently reveals that she knows about events in the future, making Cheng Yuanzhi wary. At the same time, a subtle affection begins to grow between them, and Xiaoxuan realizes she has fallen for this upright officer, across the boundaries of time.
Xu Manli, the daughter of Cheng Yuanzhi's superior, is hostile toward Xiaoxuan and secretly investigates her identity. Meanwhile, Xiaoxuan discovers that Cheng Yuanzhi is about to be drawn into a dangerous mission, one that, according to historical records, may cost him his life.
