The story revolves around the 1990s, where the citizens of Seoul were gripped with a paralyzing fear after a series of brutal attacks and murders occurred. The habits of striking randomly made it impossible for the detectives to predict the criminals next move.
Aware of the American F.B.I. and its successful use of criminal profilers to identify serial killers, Gook Young Soo recruits Song Ha Young, a quiet, reserved, incredibly perceptive former detective for his team. Gook believes using this new psychological method will give the police an edge in capturing these killers.

Well I'll be honest, the first episode wasn't amazing in the sense that, me as a viewer, I wasn't captivated by the story. The first episode is supposed to do this to make the viewer want to find out more, but the show lacked in this as it was too slow for me. That's why I had only seen the first episode, and paused this series until I resumed it weeks/months later because I was bored.

Now, I want to establish that the series separates itself from other thrillers for several reasons.

First of all, its pacing, we discover a lot of detective work (door to door, documentation and archiving ... etc.) so it gives a more realistic impression of really observing what is surely the daily life of the police at that time, and that may be redundant. I have to say that the show is really about two episodes long for each killer in average, with the full story, starting with the POV of the killer and his victims, the police work, the arrest, and the aftermath - when they're in jail. It's really quite a process, and sometimes the show made us jump months or even years forward to showcase the realism and the time it takes for investigations to be solved.

Secondly, I would say it's really a series that was focused on showing how the Korean police integrated profilers and how they helped, it's a long process again, with many backlashes coming from superiors or colleagues who at that time didn't see why profiling a killer could help them solve cases. So there are a lot thrilling moments, I wouldn't lie, but it's really a series that focuses on the police and historical aspect of such an approach.
It reminds me of models, in the fashion industry, runway models are chosen for their very thin, almost characterless features and bodies to showcase the clothes. Well here, I would say the actors were good in their roles but ultimately they were more part of a bigger picture where the story was more important than the characters.

And lately the show hasn't been overly focused on drama, like no big shenanigans from superiors or rich, no backstabbing between friends or colleagues, no revenge, no love dramas, no overly character strong and intelligent. All these elements that are generally part of drama thrillers in Korean, here have been set aside to focus on realism and tell the story - a little fictionalized - of profilers in the police.

I would like to mention, also, that all the actors did a good job of bringing their characters to life, especially actor Kim Nam Gil who played the main role of Song Ha Young, showing how much this kind of profession - profiling - weighs on these people, and that it requires a certain mind, composure and discipline, and above all intelligence.

So I recommend sticking with the show after the first episode, I believe the story is very well written - the characters and the story, especially from a detective perspective, and despiste the sometimes slow pacing, realism cover that well.
It's really a series to see, and I must say that I really enjoyed it, the killers were real monsters, not romanticized, who often committed the worst crimes.