Wow! This drama is the best action/suspense drama I have ever seen. From the writing to the execution of the story to the acting. It is simply brilliant! So many writers of this genre tend to rely heavily on the action and thrill parts, while slacking off and leaving the story with a lot of plot holes. Not the case here! The story is tight and if there were flaws, they were so miniscule that I did not notice. It also is one of the only dramas around that actually has a believable psychopath character. Trust me. Psychopaths are not sweet and sexy deep down. They are cold, ruthless and lack empahy towards others. Here, it is shown exactly like that. The acting was superb. Every actor, from the main leads to the supporting characters were incredible. I am especially impressed by Kim Young Kwang's performance. I have always liked him, but here he shines. His character is very complex and right from the beginning he steals the spotlight from the other leads with his charisma and presence. My favorite scenes of him are the close ups of the face when he laughs, and in his eyes, you can see that the character is somewhat insane. Definitely one of, if not the best, lead male performances I have seen this year. I also want to remark about two of the other lead actors. Kim Seul Gi was also already a well liked actress for me, but she really impressed me here. As someone who suffers from social anxiety disorder myself ( though not nearly as extreme as her character here), I thought she was very authentic, right down to the spot on panic attacks. This was the most honest portrayl of it I have seen in dramas. Also Key. Him being an idol, I was not expecting much in the way of acting chops from this young man. Well, he proved me wrong, alright. He most certainly is one to watch for in future projects. In conclusion, if you are looking for a good action/suspense drama, this one is the one for you. In my opinion, it is darn near perfect. Check it out. 10/10