Chen Huaian, a modern-day man who travels back in time with an endless lifespan and the strength of a legendary overlord, arrives in the ninth year of the Wude era and finds himself caught up in the Crown Prince's faction on the eve of the Xuanwu Gate Incident. After failing to persuade Li Jiancheng, he takes Wei Zheng with him and deliberately has them both imprisoned to escape disaster. Following the coup, Chen Huaian earns the favor of influential figures and becomes an instructor at the Hongwen Academy, teaching the Crown Prince and the sons of powerful officials. Using his advanced knowledge, he warns of the Turkic threat, invents distilled liquor, improves the curved-shaft plow to amass wealth and supplies, and stands up to the corrupt official Pei Ji. As he navigates the imperial court and the streets, he must protect the secret of his immortality while quietly reshaping the course of the Zhenguan era.