Li Chengqian, a modern university student, is reading a historical novel about the Tang dynasty in a library when a sudden rift in space-time appears and unexpectedly transports him into the book. He awakens in the body of Li Chengqian, the crown prince of the Tang dynasty during the Zhenguan era. He arrives at a perilous moment: his original counterpart has just broken his leg in a horseback riding accident and can barely move, while Empress Zhangsun, his greatest source of support, has already died of illness.