I've seen my fair share of psychological crime TV shows in my life and I don't think that this was anything special, but I still enjoyed it. There were a couple of plot twists which I thought to be quite predictable, but it was still quite thrilling to watch. I think that this is one of Park Bo-gum's better works. His acting was fantastic and could convey so much emotion with just his eyes. Also, I personally don't think most idols make good actors, but D.O.'s performance was outstanding. The main cast also did a fantastic job.

Cha Ji-an's backstory seemed a little unnecessary to me, though I guess they had to write it as such in order to introduce the two characters together. I think something else should have led to their meeting instead. I really liked the Lee Joon Young's backstory though. I think it perfectly encapsulates childhood trauma and neglect can do to a young mind. The concept of the "critical period" was very well executed in the drama, which is why I still enjoyed the drama a lot even though the plot was nothing special. I think "You" (American Netflix show) or "Partners for Justice" (K-drama) might have done a better job as psychological thriller dramas but this one really isn't all that bad.

Nothing special about the OSTs, I don't remember disliking or loving it in particular. Overall, a pretty good crime drama (though nothing special) with some quirks here and there.

In summary:
What i liked - Cast, acting, some aspects of the plot were quite interesting
What i disliked - Cha Ji-an's backstory

Star of the show: Park Bo-gum, Seo In-guk, Do Kyung-soo

Rating: 8.5/10
Watch if you enjoy psychological dramas or have some understanding of socialisation and developmental psychology