In 210 BCE, Qin Shi Huang planned to inspect the southeastern regions of his empire on his fifth imperial tour. His entourage included Prime Minister Li Si, Chief Eunuch Zhao Gao, and his beloved youngest son Hu Hai. The grand procession departed from Xianyang in October, first arriving at Yunmeng (near present-day Xiaogan in central Hubei Province). There, Qin Shi Huang paid homage to Emperor Shun from afar at Mount Jiuyi, then entered Zhejiang via Danyang, crossed the Qiantang River, and reached Kuaiji Commandery (in present-day Suzhou, Jiangsu). On Mount Kuaiji, he sacrificed to Yu the Great and had his achievements inscribed on a large stone. The tour then headed north from Kuaiji to Langya (present-day Jiaonan, Shandong), continued north to Mount Rongcheng (within present-day Weihai, Shandong), and then to Zhifu (northern Shandong Peninsula). At this point, the procession turned westward toward Xianyang. When they reached Pingyuan Ford (south of present-day Pingyuan, Shandong), Qin Shi Huang collapsed from exhaustion and the rigors of the long journey. Despite multiple diagnoses and treatments by the imperial physicians, his condition did not improve, so he was placed in the Shaqiu Palace (northwest of present-day Guangzong, Hebei) to recuperate.
Emperor Qin Shi Huang knew that his illness this time was very serious and feared he would not live much longer, so he quickly summoned Zhao Gao to his side and ordered him to write a letter to his eldest son, Fusu. At that time, Fusu was stationed in Shangjun with General Meng Tian and their army, and Qin Shi Huang intended to pass the throne to him. The letter instructed Fusu to rush back to Xianyang as soon as possible, and if the emperor unfortunately passed away, Fusu was to preside over the funeral arrangements.
However, Qin Shi Huang died with regret before this letter could reach Fusu's hands.
Zhao Gao had excellent handwriting and was well-versed in legal codes and classical texts, so Qin Shi Huang valued him highly, appointing him not only as the Director of the Imperial Carriage Bureau but also as the teacher of Hu Hai, which led to a very close bond between Zhao Gao and Hu Hai, with Hu Hai consulting Zhao Gao on every matter.
After the First Emperor of Qin passed away, Zhao Gao held the imperial edict in his hands, his emotions a mix of excitement and anxiety. He had always harbored great ambitions, wanting to install an emperor he could control. Fusu was certainly not an option—first, because their relationship was poor, and second, because Fusu had a grudge against Meng Tian. If Fusu ascended the throne, Zhao Gao would surely meet a bad end. Huhai, on the other hand, was the perfect choice. With this in mind, Zhao Gao went to discuss the matter with Huhai. Although Huhai was already twenty years old at the time, he lacked strategic thinking and was heavily dependent on Zhao Gao. Under Zhao Gao's smooth talk, Huhai quickly agreed. Zhao Gao then went to see Prime Minister Li Si, as such a major affair could not be kept from him. Initially, Li Si refused, but under Zhao Gao's threats and temptations, he gave in.
So Zhao Gao and Li Si secretly altered the imperial edict, appointing Hu Hai as the heir, and wrote a letter to Fusu, using the tone of Qin Shi Huang to demand that Fusu and Meng Tian commit suicide. They then falsely claimed to the outside world that the First Emperor was too weak to travel and that all matters would be handled through them, thus covering up the truth all the way back to Xianyang.
Soon after, news of Fusu and Meng Tian's deaths arrived, and the three of them finally announced to the world that Qin Shi Huang had passed away, supporting Hu Hai as the Second Emperor of Qin. The ministers were kept in the dark, so naturally no one suspected anything. After Hu Hai ascended the throne, Li Si remained as Prime Minister, and Zhao Gao was not promoted either, but real power in the court was firmly held by Zhao Gao. Those who had previously submitted memorials impeaching Zhao Gao were reported to Hu Hai by him with exaggerated and fabricated accusations, and Hu Hai, without any consideration, had all those high-ranking officials executed. The Second Emperor of Qin, fearing that his usurpation would be exposed, did not even spare his own siblings, all of whom were put to death. Li Si, unable to bear it, spoke a few words, and was sentenced to death by the Second Emperor, suffering the punishment of waist cutting, with his entire family also executed. In the end, Zhao Gao smoothly rose to the position of Prime Minister.