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Undercover High School starring Jin Ki-joo and Seo Kang-joon aired episodes 7 and 8 on March 14 and 15, 2025, on MBC. It tells the story of Jeong Hae-seong, played by Seo Kang-joon, an NIS agent who infiltrates a school to complete a mission.
His homeroom teacher, Oh Su-ah, depicted by Jin Ki-joo, is working on a contract with the goal of becoming a full-time teacher. Oh Su-ah is always suspicious of Jeong Hae-seong, but at times, he reminds her of her first love.
In Undercover High School episode 7, Oh Su-ah decides to help the NIS team with Jeong Hae-seong to solve the third legendary mystery. Jeong Hae-seong was against her doing so, she told him that she was trying to prove herself to a former student that she could also protect her students.
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As the two went inside director Seo Myeong-joo's office to play the piano, they learned that a specific key did not make a sound and that nothing happened. NIS team leader Ahn Seok-ho asked them to abort the task and leave the place.
Jeong Hae-seong deleted the traces of their presence in the office by deleting the record in Seo Myeong-joo's computer. He learned the shocking truth behind the overall mission to find the gold and that Seo Myeong-joo had a mole in the NIS. The mole was the one who assigned Jeong Hae-seong on this mission upon her orders to find the gold bars.
Undercover High School ep 7-8 recap: Jeong Hae-seong joins Oh Su-ah in finding dirt on Seo Myeong-joo
In Undercover High School episode 7, Lee Ye-na and Jeong Hae-seong become the new models of the school. Jeong Hae-seong apologized to Ahn Yu-jeong for meddling in her issues with Lee Ye-na. Ahn Yu-jeong explained to him that she's suffering and acts harsh at times, but she is a good friend.
Later, at the Byeongmun Night party, Seo Myeong-joo held a private meeting to tell the parents with powerful backgrounds how she planned to build the edu-city with the top 1% of students in the country. Lee Ye-na and Ahn Yu-jeong drifted apart due to Lee Ye-na’s continued harsh behavior towards Ahn Yu-jeong.
In Undercover High School episode 8, Jeong Hae-seong was taken aback by learning about the mole and Seo Myeong-joo, and despite Oh Su-ah solving the puzzle of the third legend story, he did not pay it much attention. Later, Oh Su-ah took him for a drink, and he opened up, saying that he could not trust anyone after this incident.
Oh Su-ah told her to find only one person to trust and that she is there for him. Jeong Hae-seong told her that he was Jeong Shi-hyeon, her elementary school friend. This surprised her, but they grew closer after this.
Lee Ye-na saw Lee Seung-jae and his father talking about tampering with grades on Byeongmun Night. She told him to come clean about it. He was irritated and told her that Seo Myeong-joo tampered with the grades of students with powerful backgrounds and received help from their parents to build the Edu-city.
On the other hand, Oh Su-ah got Lee Seung-jae’s card, which had a link on it, and decided to return it to him. However, she opened it to see the plan for tampering with the scores of the upcoming exams. She asked Jeong Hae-seong to help her, but he denied her, as he himself was not sure about the mission he was working on. It would get him expelled if they were caught.
Jeong Hae-seong saw his sister, Ahn Yu-jeong, studying hard to become an agent like him and her father, Ahn Seok-ho. He decided to help Oh Su-ah find evidence about it. That same night, he put a tracker under the table of the restaurant where Seo Myeong-joo, Lee Seung-jae, and his father met to discuss their plan in detail.
From this conversation, Jeong Hae-seong learned that Seo Myeong-joo knew about Oh Su-ah accessing the link and that she would be in danger. He immediately went to the school where Oh Su-ah was looking into old documents as the link was no longer accessible. Jeong Hae-seong asked her to work with him and took her to his place so she would be safe there.
Later, in Undercover High School episode 8, Ahn Seok-ho was furious to see Jeong Hae-seong working on something else and not focusing on the mission. Jeong Hae-seong confronted him, saying he was too obsessed about the gold, and told her that the grades were going to affect Ahn Yu-jeong.
Ahn Seok-ho told him to cease this and work on the mission alone; he gave him an order as his team leader and not Ahn Yu-jeong's father.
The NIS director, Kim, saw them arguing on the rooftop and asked them to go inside the office. The next day in Undercover High School, Jeong Hae-seong received a text from Ahn Seok-ho that they had to cease the mission and wrap up in a week. Jeong Hae-seong informed Oh Su-ah, but he had to stay in school if he wanted to learn about his missing father and to stop Seo Myeong-joo.
Jeong Hae-seong saw Seo Myeong-joo having lunch at the school cafeteria and asked her if he could sit with her. He provokes Seo Myeong-joo about the gym and the last legend story. Seo Myeong-joo called the mole to get rid of Jeong Hae-seong as soon as possible because no one knew about the gym.
As Undercover High School episode 8 progressed, Lee Ye-na went to Ahn Yu-jeong's house after getting into an argument with Seo Myeong-joo about the grades. Seo Myeong-joo kept asking her to get rid of Ahn Yu-jeong and that she made Lee Ye-na work hard so that nobody would be suspicious about it.
Lee Ye-na told her that she was her friend. At Ahn Yu-jeong's place, Lee Ye-na and she had dinner together but were awkward. Lee Ye-na told her that she was thankful before leaving.
Undercover High School episode 8 ended with the scene where Oh Su-ah saw an intruder at Jeong Hae-seong’s house where they were working together. Later, when Jeong Hae-seong reached home, he saw Oh Su-ah had fainted on the floor.
Meanwhile, Undercover High School airs every Friday and Saturday on MBC at 9:50 pm KST.
