In 228 AD, the Shu army defeated Wei in the Northern Expedition. According to the analysis by the intelligence department of the state of Shu, the false information that led to the misjudgment of the Shu army was sent by Chen Gong, a senior spy lurking in Wei. Shu's counterintelligence expert Xun Xu was ordered to infiltrate Wei to investigate Chen Gong. Chen Gong passed Xun Xu's investigation. They found that inside the intelligence department of Shu, there had been an undercover Cao Wei, code named "Candle Dragon". "Candle Dragon" not only replaced Chen Gong's intelligence, but also planned to steal the design of Shu's repeated crossbow. Tu's secret operation started the "Qingping Plan" to create chaos in Shu. Xun Xu returned to Shu Kingdom, ready to work together with Chen Gong to find out the true body of "Candle Dragon". Xun Xu successfully prevented Wei from stealing the secrets of the repeated crossbow, and found the traitor hidden in the intelligence department of Shu. Chen Gong returned to Shu after his undercover career, and went through many tests with Xun Xu, and finally revealed the truth behind the "Qingping Plan". In the face of the righteousness of the family and the country, Xun Xu and Chen Gong made the right choice at an important juncture, cracked the enemy's sinister conspiracy, and maintained the stability and unity of the country.