I absolutely loved this drama. I gave it a 10 which I usually never do. I found myself... well, cheering the devil on, which sounds kind of weird. He had my sympathy, while the people getting killed off I mostly felt indifferent towards. This series really made me question my morals, since I was on the side of the one getting revenge. The actors... awesome. Especially Joo Ji Hoon. Since his character mostly kept a straight face during this drama, he truly got the opportunity to act minimalistically; and he did that very well; while keeping a mostly straight face and the tone of his voice always even, he managed to convey emotions just with his eyes and micro-expressions. I wasn't really bored at any point, the police investigations weren't so interesting for me, but all the parts with the 3 main actors I really looked forward to. And while I usually hate, hate, HATE flashbacks and childhood stories, I found myself looking towards them in this drama. I would recommend this to anyone who wishes to question their morals from time to time, and wants to watch some great acting. (If you like this, also check out the Japanese remake, Maou. For me it's nowhere as near as great as this one but it's also very good and has good actors in it.)