On the day of Ma Yunfei and Gao Han's wedding, an uninvited guest came - Lao Yu, an old friend of the "No. 5 Special Agent Group", and begged them to come out again to perform a task that no one else could accomplish: to track down the double agent Yoshikawa Takeo who stole American nuclear weapons information. For this reason, Gao Han became a runaway bride and followed Ouyang Jianping and Li Zhibo to Yunnan to accept the mission. Ma Yunfei and He Jian were also forced to come out of the mountains, so the five members of the "No. 5 Special Agent Group": language expert Ouyang Jianping, blasting expert Li Zhibo, agent Ma Yunfei, cryptographer Gao Han, and "thief" He Jian once again assembled on the front line. At the same time, the Japanese sent their trump card, Sakai Asaka - she is Sakai Mieko's biological sister, a senior female spy with even more vicious and fierce tactics. The "Agent Team No. 5" had a bad start and was framed and imprisoned by Yoshikawa Takeo's accomplice who had not yet been exposed. No. 5 had no choice but to escape from prison... While evading the pursuit of the US military, they pursued Yoshikawa Takeo, and finally found the traitor in the US military and found the stolen nuclear weapons information before Sakai Asaka. The war intensified, and soldiers on the front battlefield were infected with the virus on a large scale. The Agent Team No. 5 was ordered to investigate, and missed the culprit of the virus station, Hashimoto, on the way. Hashimoto was also a Frankenstein who regarded scientific experiments as above all else. He injected Gao Han with the virus, kidnapped her as a test subject, and carefully protected and studied her all the way. Ma Yunfei, Li Zhibo, and He Jian went deep into the Yunnan-Myanmar border. After a difficult jungle pursuit, they touched the enemy's biochemical base in Myanmar. At this time, Gao Han almost gave his life to get the virus serum and rescue a large number of soldiers on the front line. The war was urgent and supplies were in short supply on the front battlefield. Chiang Kai-shek set his sights on the munitions that Yan Xishan had privately stored in his early years. Yan Xishan refused to provide Chiang Kai-shek with military supplies on the grounds that Li Yang, the builder of the arsenal, was missing. Dai Li had to turn to the No. 5 Special Agent Group again and asked Ma Yunfei and four others to sneak into Shanxi to find the whereabouts of Li Yang, the builder of the arsenal. The No. 5 Special Agent Group took advantage of the Japanese commander Yoshihiro Kazama's love of Chinese painting and stole ancient famous paintings from Chiang Kai-shek's home as bait to lure Yoshihiro Kazama. By selling paintings, they went deep into the headquarters where Yoshihiro Kazama lived and took the opportunity to secretly photograph the battle records and roster of the Japanese Jinzhong Battle. At this time, Sakai also came. Ma Yunfei cleverly maneuvered and successfully escaped from the Japanese headquarters on the eve of being discovered. No. 5 followed the map, and Ma Yunfei and He Jian entered Kangkeng Guihua Prison through false confessions. After much trouble, the two finally gained the trust of Zhu Fei, the leader of the prisoners in the prison, and assisted him in escaping from prison. Zhu Fei's operation failed. Before he died, he told Ma Yunfei that he was Li Yang. No. 5 finally found the arsenal before the Japanese. The No. 5 agent team returned to Chongqing with Song Meiling's beloved Chinese painting, ready to return it intact. As soon as they got off the plane, they ran into Chennault, the captain of the American Flying Tigers who came to China for assistance, who was attacked at the airport. The No. 5 agent team did not have time to get away and was blocked at the door by Lao Yu and Dai Li. No. 5 started from the shooting scene at Chongqing Airport. Using knowledge of physics, firearms, psychology, reasoning and deduction, etc., he restored the shooting scene from extremely limited clues, and followed the clues to completely disintegrate the Japanese assassination plot. After revealing the truth, Ma Yunfei and others were ordered to protect Chennault to Chongqing; Mrs. Chennault also invited American security consultant Roth to ensure Chennault's safety. After Roth arrived, he criticized the actions of Ma Yunfei and others, and the endless accidents also put the No. 5 agent team into a passive position again and again. After many twists and turns, Ma Yunfei and others found that the real culprit of all the incidents was security consultant Roth - this guy was an imposter. The No. 5 Special Agent Group received an invitation from General Sun Liren of the Chinese Expeditionary Force to send an important river map to Myanmar. They were accompanied by Cui Yuanyuan, an accompanying reporter, and Ma Yunfei's old classmate. Gao Han was jealous of this. They didn't know that Cui Yuanyuan was actually Sakai Asaka in disguise. Sakai killed and pretended to be Cui Yuanyuan to follow No. 5 in order to sneak into the expeditionary base and cooperate with Japanese bombers to carry out bombing. Only Gao Han saw through Cui Yuanyuan's face, but others thought she was jealous and suspicious and didn't believe her words. When everyone was sent into the trap by the disguised Sakai one by one, and the bonfire guiding the Japanese bombers was about to be ignited, Ouyang Jianping, who had been away from the team for a long time, arrived with Chennault's rescue. Sakai Asaka repeated her sister's fate, and the No. 5 Special Agent Group reunited again, but Gao Han and Ma Yunfei, a couple, became strangers.