Seo Kang-jun and Jin Ki-joo were shocked by the return of Kim Shin-rok in 'Undercover High School.'

In the broadcast on the 21st of MBC's Friday-Saturday drama 'Undercover High School,' Seo Myung-joo (played by Kim Shin-rok) was depicted tearing off Jeong Hae-sung's (played by Seo Kang-jun) name tag.

On that day, Oh Soo-a (played by Jin Ki-joo) faced an intruder at Jeong Hae-sung's house. Oh Soo-a confronted the intruder, asking, 'Who are you? Why are you here?' The intruder threatened Oh Soo-a with a blade. Ultimately, Oh Soo-a collapsed after being stabbed. Jeong Hae-sung, who arrived home late, discovered Oh Soo-a and hurried her to the hospital. Feeling guilty, Jeong Hae-sung apologized to Oh Soo-a, who was lying down after surgery, saying, 'I’m sorry. I’m sorry I couldn’t protect you.' At that moment, Oh Soo-a regained consciousness and smiled, saying, 'If you’re really sorry, be nice to me.' Jeong Hae-sung expressed his relief, saying, 'Are you okay? I was worried. Thank goodness.'

Oh Soo-a informed Jeong Hae-sung that the perpetrator of the school’s grade fraud was fellow teacher Lee Jun-ho (played by Noh Jong-hyun). At the same time, Koh Young-hoon (played by Jo Bok-rae) called Jeong Hae-sung to report the DNA analysis results found at the scene, indicating it was Lee Jun-ho. Jeong Hae-sung instructed, 'So the person who was at my house was Lee Jun-ho? For now, keep close surveillance on Lee Jun-ho. Don’t tell the head of the team. I’ll talk to him.'

Thus, Jeong Hae-sung realized that Lee Jun-ho had stolen his father's notebook from his house. At the same time, Lee Jun-ho asked while handing over the notebook, 'I heard there was an incident last night. How do you plan to handle it?' Lee Jun-ho added, 'Please keep your promise. If I follow your orders, ensure my name won't come up in the grade fraud case. Promise not to make me manipulate my grades anymore. I won’t even ask what the notebook is. I also won’t ask about Jeong Hae-sung's true identity. Instead, I will trust that I will be protected.'

Seo Myung-joo asked, 'Why me?' Lee Jun-ho replied, 'If I get caught by the police, it would be troublesome for the chairman.' To this, Seo Myung-joo responded, 'Right. Teacher Lee Jun-ho, this is it for you. You’ve worked hard during this time.'

However, Seo Myung-joo failed to gather the last hint about the terrifying rumor from the notebook. He recalled Jeong Hae-sung mentioning the gym while in the cafeteria and angrily questioned, 'So the answer is just myself?' He then attempted to eliminate Lee Jun-ho through Principal Park Jae-mun (played by Park Jin-woo), but failed due to Jeong Hae-sung's interference.

Jeong Hae-sung had previously suspected Head of Team An (played by Jeon Bae-su) of being Seo Myung-joo's accomplice. With the misunderstanding resolved, he apologized to Head of Team An, vowing, 'I will complete the mission assigned to Agent Jung Jae-hyun 22 years ago. I will find everything. The gold bullion and my father too.'

Afterward, Jeong Hae-sung exposed Seo Myung-joo's grade fraud case, starting with Lee Jun-ho's confession. Principal Park Jae-mun and Seo Myung-joo were arrested by the police. Director Kim (played by Lee Seo-hwan) appeared before Seo Myung-joo in the interrogation room, stating, 'The situation isn't very favorable. It seems the chairman's education city project has also fallen through,' and asked, 'Is there a plan to overcome this situation?'

When Seo Myung-joo couldn't speak, Director Kim remarked, 'There’s no plan, and there’s no way for us to keep our promise, so this is where we end up. I know a highly skilled lawyer who also excels in writing confession letters.' To this, Seo Myung-joo ominously laughed and said, 'How far do you think a madwoman who lost everything will go, without fear?'

Unfailingly, Jeong Hae-sung attended school, focused on solving the final horror story. Through Lee Dong-min (played by Shin Jun-hang), he heard, 'This might sound ridiculous, but they say the school is cursed. The last person to learn the horror story will experience a vanishing phenomenon. One day, suddenly, they disappear without a trace.' Moreover, Jeong Hae-sung also obtained hints through the school's history.

Meanwhile, as the scholarship officers visited the hospital, Seo Myung-joo and Principal Park Jae-mun made a reappearance that surprised everyone. Seo Myung-joo approached Oh Soo-a and said, 'I heard about what happened. You almost died. From now on, you must be especially careful.'

Jeong Hae-sung also heard the news and rushed over. Seo Myung-joo remarked to Jeong Hae-sung, 'We’ve been seeing each other often lately,' and added, 'But what to do? The student games end here,' while tearing off the name tag, heightening the tension.

[Photo] Capture from 'Undercover High School' broadcast.

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