So far the theory that makes the most sense to me is that it's somehow the ML. At this stage(Which can change because we're only 4 episodes in) I don't see any other way to get the FL and him to have a romance, plus him being a random external hire and trying to act just how corrupt company CEO would want him to is a bit sus.

I feel like it’s almost obvious that it’s Bok-hee. The deceased president even basically hinted at as much when he met with Geum-bo. But the fact that Geum-bo hasn’t suspected her at all makes it seem even more likely.

Btw is yippe bad or good? 

Whoever it may be.. 

It could be anyone... it is certainly not the Queen Bee from the dorm... 

It could be new CEO and is probably the most qualified candidate... The new CEO is doing something shady ... either to steal or to catch criminals...   

It could be Ms Song, the older assistant who lives in the house... She is either stealing from the company, and I think that is the more obvious answer since she is on the killing of Ms. Kim... 

.... it could be Mr Lee...  :) as a computer hacker :) 

....  it could be even Albert, and esp after he started chasing FL ... TO me, at the start of ep 6 during dinner, it looked like Albert knew something already 

I think it's Bang Jin Mok one of the Risk Management team leads as he seems to know his way around and also that he's a wiz at cleaning up the books. Although he appears to do nothing, a lot of the other team members seem to still look up to him and take his guidance. I think he's going to be the dark horse.