I took upon watching this drama for two reasons. First of all - Lee Joon, and secondly I really love TV series likes. I'm a huge fan of American TV masterpiece (to my mind at least) Criminal Minds, which focuses on FBI catching serial killers and psychos, so I wanted to see a Korean take on dealing with mad criminals. The drama left me with mixed feelings. Maybe I am too used to western ways of investigation when dealing with serial killers, but the way how the investigation was portrayed here seemed very messy, chaotic, illogical and more corrupting evidences and witnesses than actually using them to catch the killer. It might be 'the Korean way' of working, as I have noticed such illogical things in other dramas too, but it was still hard to grasp. The investigation took a semi-decent turn only near the end of the drama and, well, better late than never. The whole plot was rather interesting - the connection between characters, the search for the reap GapDong, the mystery behind that persona - that all was captivating. It did have its boring moments, as no investigation is exciting all the time, but it was bearable. What made me the happiest, but also the saddest was the acting. I was very, very happy about Lee Joon's acting. His acting was simply superb to my mind as he was playing a psychopathic murderer and indeed showed the characters madness trough his acting. He was acting even with the smallest muscle of of his face and seeing him in action - going from a sweet smile to a mad-mans grin in 0.000001 second - was amazing. Yoo SangHyn though left me disappointed, as he massively overdid his character. Okay, be the 'Mad Monk', show that you are not entirely normal either, as it was, as far as I understood, implied in the story, but, please, keep it real. He is a great actor, that I know, but this time, I think, he took the wrong path in portraying his character. What a pity. The ladies cried a bit too much one the other half of the series. To my mind you can show grief, fear, sadness and joy in many more ways than just trough tears. And a single-tear crying is no longer convincing to me. All in all the drama was watchable and at some points even enjoyable. I doubt I would watch it again, but for one-time watching it was even very okay. If investigation, crimes, serial killers and all those 'nice' things are for you, this drama is for you.