There're are reviews calling it a mess or too complicated. No, it is not if you use your brain properly. this series has one of the best planned storyline. it does have plots, but it is worth it. Anyone calling it a mess just cannot keep up with this pace, and i think such people need to avoid such stories that just messes up with their head because they cannot seem to understand the storyline which is literally their problem. (In simple terms, THEY ARE JUST TOO DUMB).
** The main character's acting is top-notch. The science approach was well detailed (i'm a biomed student, so yeah i found it intriguing). The suspense, thriller, all of it keeps you on the edge of the seat. As for me, i was able to figure out who the psychopath was because i was into it, and it was not a mess at all. There's sad scenes that can tear you up if you're emotional, and really unexpected turns, but foof, this is the *the* best. After watching this, i haven't been able to find another series that matches the thriller, details, suspense, and overall storyline. I promise you that you will not regret it if you watch it, (also do not forget to get into it- the best part!)

***the only TV drama from South Korea to be nominated for the international Panorama Category at the 11th Annual Series Mania 2021.
Lee-seungi earned the Grand Award (Daesang) for best actor in TV category at the 6th Asia Artist Awards.
best supporting actor award as well.