Shen Yan, a modern hermit, lives in seclusion in Jinyun, Zhejiang, with a strong artificial intelligence "Lingxi" and a precision manufacturing center. One day, the five-year-old princess "Sizi" (Princess Li Mingda of Jinyang) during the Zhenguan period of the Tang Dynasty accidentally traveled to the window of his study. This little girl who should have died of illness at the age of twelve completely changed the fate of two worlds with her softness and innocence.
Shen Yan devoted all his efforts to protecting Si Zi, taking her to taste modern food and experience warm daily life. Every time Sizi returned to the Tang Dynasty, he would bring back fairy food and gifts from the "Bai Yujing Wonderland", making the royal family gradually accept this mysterious existence. With the addition of Princess Li Lizhi of Changle and Princess Chengyang, Shen Yan established a deep bond with the Tang royal family.
In the name of "Bai Yujing Hermit", he rescued Empress Changsun, guided the inferior prince Li Chengqian, built "Yongning New City" that completely replicated the modern city, and improved firearms to fight off the Turks. As they got along again and again, he gradually fell in love with the gentle and dignified Princess Li Lizhi of Changle, and finally broke Li Shimin's original political marriage and was granted a marriage contract.
The story uses "Si Zi" as the link between time and space, Shen Yan's modern abilities as the support, and the original intention of "sending Si Zi a prosperous Tang Dynasty" as the original intention. It finally creates the prosperous era of Zhenguan and rewrites the historical tragedy - Si Zi grows up safely, Li Lizhi escapes the fate of premature death, Li Chengqian becomes the Mingjun, and the Tang Dynasty enters unprecedented prosperity.
