One summer night in Shanghai, Zong Ying bumps into an unexpected visitor at home who claims to also be the owner of an old apartment No. 699 in Shanghai. Every night, he time travels from 1937 to modern times and goes back by the morning. He even has proof of his identity as an attorney of the Republic of China.

Although Sheng Qing Rang tried to convince her that he was from another time period, the level-headed Zong Ying was quick to brush it off as nonsense. Yet when he disappears before her eyes, she has no choice but to begin accepting the fact. What began as an accidental encounter has found purpose.