
To answer your concerns it’s because of the author’s way of writing things. The “I’m going to make you think this is the plot BUT SIKE”, based on the chapter in the novel we’re only about 1/3 of the way through and there’s a lot more mystery to look forward to such as the garden of Eden, the “vaccine”, the cure and the relationship of the second master to the main cast and the 4 rivers will all be revealed and Dr.Oh’s death is only the tip of the ice berg. Just keep reading I promise it’ll be good (๑•ㅂ•)و✧

Don't worry, I'm totally set on continuing with this story, it's great and outside of this I had no issues with the plot whatsoever (except for chapter 2-3, but we don't talk about chapter 2-3). I really like this and I think the mystery is great, I just wish the reveal was a little better, even if it's not that consequential to the entire plot. Still, thanks for letting me know where we're at, I can't wait to see how it develops! :)
Uuuughhhh..... It's usually a really tense and interesting story, which is why this writing decision is so disappointing!
The investigation being dr. Oh's death was a hugely important plot point, serving to turn Dr. Seok into an active protagonist, rather than a passive bystander.
The investigation was what drove them to spend time together.
The circumstances around his death were set up as specific clues, like you'd do in a mystery. We weren't just told "his death is suspicious", we were told where he stood when he was shot, who had access to the lab, the alibis of other doctors, the time of death and that it was meddled with.
The Garden of Eden and it's leader has also been a huge deal! We've slowly been getting fragments of information about what they are, what are they after, why are they interested in Dr. Seok and how are they connected to Dr. Oh's death.
My main point being, that while not tagged as such, this whole time the plot has been clearly centered around a mystery. Why, oh why, would they decide to suddenly reveal the entire mystery to me, without the protagonist present, without any tension, being delivered by a guy we've literally never met before. Why are we immediately given all the answers and why are the main culprits behind these mysteries two guys, who not only did we not know who they are, until last chapter, we literally didn't even know they exist. Sorry, the main culprits being the two leaders would've been a lot more interesting had it been set up better beforehand.
I kind of get revealing the truth behind Oh's death, as the clues and conclusion were kind of already there (But I'd do it in a more tense and relevant way!), but whyyyyyyyyyy reveal who's the leader of Eden. There was no need for that aghhhhhhh. Sorry.