Jin Ki-joo and Seo Kang-joon | Photo from @mbcdrama_now

School K-dramas are refreshing to watch as they often offer a slice-of-life take on storytelling. In Undercover High School, however, you get a slice of that, a generous portion of action-mystery, and sprinkles of romance and humor.

Set at the fictional Byeongmun High School, the series stars Seo Kang-joon as Jeong Hae-seong (an NIS agent tasked to go undercover in a school on a mission to find missing gold bars) and Jin Ki-joo as Oh Su-a, Hae-seong's homeroom teacher. As the story unfolds, we discover their connection doesn't stop there and that there are deeper layers and backstories to unpack. And these plot twists, alongside the familiar stories of bullying and hierarchy in school, make the series more binge-worthy. 

Asked about the relevant themes in Undercover High School that he found most compelling, Seo Kang-joon told Metro.Style, "I deeply resonated with the themes of growth and the injustices of the world that this drama seeks to convey. It made me reflect on how we should face life and its moments, despite the unfairness around us. Even if certain things may never change, I want to live with the determination to resist and push back against what is wrong. That’s exactly the kind of story this drama tells."                                     

Jin Ki-joo says she and her character don't have many similarities, sharing, "Su-a is outgoing, whereas I'm more introverted." But she resonates with Su-a's values—"especially her views on the role of schools and teachers," she mentions. 

Even with their limited interactions due to their teacher-student setup at first, the chemistry between Seo Kang-joon and Jin Ki-joo is apparent. On working with Jin Ki-joo, Seo Kang-joon shares, "Jin Ki-joo is a very honest and genuine actress. Her acting changes depending on how I deliver my lines, which made working with her incredibly fun. Plus, she has this lovable charm that makes everything feel forgivable."

The cast also includes Kim Shin-rok as Seo Myeong-ju, the chairwoman of the Byeongmun Foundation and Byeongmun High School and the mother of the student council president, Lee Ye-na (played by Kim Min-ju). With Seo Myeong-ju as the villainess in the series, Seo Kang-joon also praises the actress who brought this character to life. He says, "Kim Shin-rok, on the other hand, is like a meticulous and thorough analyst. Collaborating with her to build each scene was truly enjoyable, and she constantly made me reflect on whether I was overlooking anything in my own performance."   

But being meticulous and thorough, it seems, also applies to Seo Kang-joon in the way he approached his character as an NIS agent—a tough guy who's sexy, charismatic, and funny yet pensive, too. In the first episode, he delivered an explosive performance (quite literally) and his fight scenes in the succeeding episodes are also exciting. But it's not the physical aspect of his acting that he especially paid attention to. 

He explains, "It was challenging to portray Hae-seong because he doesn’t openly express his true feelings. People usually reveal parts of themselves when they’re alone, but his deepest emotions remain locked away, only surfacing in fleeting moments—through his gaze or in his silence. That made it particularly difficult." Even with Hae-seong's nonchalance, he's dealing with a deep sense of longing and looking for something far more precious than gold, and this lends depth to Seo Kang-joon's acting. 

"Even though his true self and emotional depth weren’t explicitly explained in the script, I made a conscious effort not to lose sight of them," he continued. "Because of this, it took me longer to fully grasp Hae-seong compared to other characters. To better understand him, I wrote something like a diary or memoir from his perspective, recalling his childhood from his current point of view. That exercise turned out to be incredibly helpful."        

Undercover High School is definitely not your typical school K-drama. It has the essential ingredients of a bingeable series, making us crave more action, romance, drama, and humor. The class is in session and so is our series marathon. 

Stream Undercover High School on Viu!