Not exactly, a spoiler...I think..

also if u have watched ep3..u should understand by now...

 rozzzol:

Its stated plainly in the synopsis of the drama

The synopsis is different everywhere I guess. In viki they have not mentioned anything like that so it feels different.

https://www.viki.com/tv/40985c-undercover-high-school

"Jeong Hae Seong, a transfer student who seems like he stepped out of a movie, quickly captures everyone's attention with his looks, charm, and smile. But beneath his perfect facade, he's not your average high schooler. Hae Seong is actually an elite NIS agent on a secret mission to uncover the hidden gold of the Joseon emperor. As he navigates high school life, he unknowingly opens up to his classmates, becoming increasingly entangled in unexpected connections. In the process, he uncovers the dark truth behind Byungmun High, a school deeply corrupted by its obsession with wealth and power. What starts as a treasure hunt soon turns into something much deeper, as Hae Seong seeks not just the gold, but also meaningful relationships. Teaming up with others, he fights back against the corruption in society. His undercover operation, filled with excitement, satisfaction, and a touch of bittersweetness, is about to begin!"

 Sheram:

I don't believe in a twin brother either. Soo Ah and Hae Seong  met when they were younger (First love). Hae Seong changed his name because he was bullied and dropped out of school so they didn't meet each other until now. But of course they don't remember each other after so many years apart.
I believe Soo Ah somewhere in episode 5-7 finds out that Hae Seong is undercover and together they investigate both the evil principal and all the ghost stories etc. In that way they come closer to each other for each day and feelings rise between them and then they finally figure out that they know each other from the past. But then Soo Ah remembers that she was hurt by him (don't know how) and they have an argument. Hmmm...well the rest...I will tell you later. :)) LOL

Sounds very accurate

 BertelYann:

May be the real romance was not Soo Ah et Hae Seong  but Yena and Yu Jeong :D Need to review all thier moments together :)

I mean, i kinda understand what u mean as i was quite surprised at Yena's character, she is not the typical evil rich friend that i see in kdramas..really happy she considered Yujeong as her chingu and not stand with her mother's evil ways...but the leads relationship was also quite fascinating...

We had just a wee bit of a GL in High School Undercover. Of course, no one might not have recognized it unless they looked closely. It could have been more. Hopefully, there will be more GL in K-dramas in the future.