Zhou Mu, a young man from modern times, accidentally travels back to the Tang Dynasty. When he wakes up, he finds himself lying in Princess Changle's bedroom. Just as he locks eyes with the princess, Emperor Taizong of Tang, Li Shimin, rushes in with a blade! At the critical moment, Zhou Mu takes out modern medicine and saves Empress Zhangsun, who is gravely ill. From then on, he is treated as an honored guest. Even more mysteriously, his every move is simultaneously displayed through a mysterious light screen before the eyes of Qin Shi Huang, Ying Zheng, and Emperor Taizu of Ming, Zhu Yuanzhang. Using his modern knowledge and technology, Zhou Mu helps three dynasties improve their technology and people's livelihoods. When a passage connecting different eras opens, the princesses step into the modern world. What changes will the three dynasties face next?