It's a really weird drama, that's the first thing that comes to my mind! :) It's unusual but so fresh, the characters are so peculiars that you would never think they could work together, but the chemestry it's so good, even if they don't meet at all. This drama is a huge mystery, too many crimes all together, it's confusing but not to the point to give up, instead, it makes you want to discover what's really happening behind the scenes.
Kyung Yi isn't introduced as the usual "detective", even before the tragedy, she had a charismatic side, even now that she's presented as a really "messed up" person, K is a character which you can always feel the presence, even if she's not present.I have to admit that I started watching this drama because of Kim Hye Joon (K), after I saw her in Chip in I really wanted to see her more and seeing her in here made me really happy, the way she portraits K is sublime. Since it's not completed yet I can't say if she's sociopathic or if she has some dissociative identity problem or something else, but the way they mix her killer side with a cute one is hilarious, yes I find her so cute!
I can confirm to you that both leads sparkle, we didn't have lots of chances to see them together, but those little moments were fire, their chemestry is no joke. The drama gives you lots of hints about their history but never revealing the complete truth, it's also happening with the background in their present, so you can only guess what happened or what's happening, the mystery is well kept and keeps you entertained.
I recommend this drama even if it has not finished, because I find it really original and different, give it a chance!