The gripping drama Undercover High School, featuring the talented Jin Ki-joo and Seo Kang-joon, captivated audiences with episodes 7 and 8, which aired on March 14 and 15, 2025, on MBC. The series follows the story of Jeong Hae-seong (Seo Kang-joon), a skilled NIS agent on a covert mission within a high school environment.
His homeroom teacher, Oh Su-ah (Jin Ki-joo), is in the midst of a contractual position, aspiring to achieve a full-time teaching role. Throughout their interactions, she often finds herself questioning Jeong Hae-seong’s motives, as he sometimes triggers memories of her first love.
Episode Highlights: The Quest for the Truth
In episode 7, the plot thickens as Oh Su-ah teams up with Jeong Hae-seong to unravel the third legendary mystery. Despite his initial objections, she insists on proving her capabilities to a former student by showcasing her commitment to protecting her current students.
During a pivotal moment in Seo Myeong-joo’s office, while attempting to play a piano, they discover a silent key, prompting NIS team leader Ahn Seok-ho to advise them to terminate their infiltration. However, Jeong Hae-seong takes preventative measures by erasing their digital footprints from the director’s computer.
In a shocking twist, he uncovers that there is a mole within the NIS, complicating the mission to recover stolen gold bars and revealing that Seo Myeong-joo had orchestrated the entire operation.
Sophomore Struggles and Hidden Shenanigans
As the storyline unfolds in episode 7, Jeong Hae-seong and Lee Ye-na are appointed as the new school models. Jeong apologizes to Ahn Yu-jeong for unintentionally stepping into her disputes with Lee Ye-na, who is struggling but is truly a steadfast friend.
During the Byeongmun Night party, Seo Myeong-joo seizes the opportunity to present her vision for an educational city aimed at nurturing the top 1% of students, further alienating Lee Ye-na from her friend Ahn Yu-jeong amidst rising tensions.
Moving into episode 8, Jeong Hae-seong is left reeling from the revelation about the mole. While Oh Su-ah makes advancement in deciphering the third legendary story, Jeong’s focus shifts to the trust issues stemming from this discovery. Over drinks, he confides in her about his struggle to trust anyone.
Oh Su-ah encourages him to confide in a single reliable person—herself. In a significant reveal, Jeong identifies himself as Jeong Shi-hyeon from her elementary school days, creating a bond between them amid the chaos.
Meanwhile, Lee Ye-na witnesses a conversation regarding grade tampering between Lee Seung-jae and his father. Confronting him, she uncovers that Seo Myeong-joo is manipulating the academic records of students from influential families.
Seeking Evidence: Shadows and Secrets
In a twist of fate, Oh Su-ah stumbles upon a card belonging to Lee Seung-jae, which she initially intends to return. However, upon viewing its contents detailing planned score manipulations, she seeks Jeong Hae-seong’s assistance. Yet, due to uncertainty surrounding his own mission, he declines, knowing that any slip could jeopardize their positions.
Moved by his sister, Ahn Yu-jeong’s dedication as she studies to become an agent, Jeong ultimately resolves to help Oh Su-ah in gathering evidence. That night, he strategically places a tracker under the restaurant table where Seo Myeong-joo, Lee Seung-jae, and his father are discussing their nefarious plans.
Through their conversation, Jeong uncovers that Seo is aware of Oh Su-ah’s activities, putting her in imminent danger. Reacting swiftly, he locates Oh Su-ah, who has been poring over documents at the school, and urges her to collaborate for safety.
As tensions escalate, Ahn Seok-ho expresses his fury over Jeong’s distractions from the primary mission, leading to a heated confrontation where Jeong emphasizes the stakes involving his sister’s education and future.
The NIS director, Kim, comes across the escalating argument, prompting them to relocate inside. Soon after, Jeong receives a distressing message from Ahn Seok-ho signaling the end of the current mission and a swift conclusion required within a week.
In a calculated move, Jeong approaches Seo Myeong-joo in the cafeteria, stirring the pot regarding her past encounters with the legends, oblivious to the impending threat against him. The pressure mounts as Seo plots to eliminate Jeong, fearing he holds secrets that could unravel her plan.
As episode 8 closes, Lee Ye-na visits Ahn Yu-jeong after a fallout with Seo Myeong-joo, displaying the lingering awkwardness of their friendship while expressing her gratitude before departing. Meanwhile, Oh Su-ah finds herself facing an unexpected intruder at Jeong Hae-seong’s home where they’ve been collaborating, culminating in a dramatic scene where Jeong discovers her unconscious on the floor.
Don’t miss the latest episodes of Undercover High School, broadcasting on Fridays and Saturdays at 9:50 PM KST exclusively on MBC.