Storyline:

this one started promising with the lead actress being a special kind of introvert autist forced extrovert if needed, being beautiful and highly intelligent in the field of programming. The idea of the new chatbot she invents fits the current times and often hopelessly automatized behaviours of modern humans.
She herself uses her chatbot and one evening decides to meet the creepy chat match instead of the normal nice guy she is talking to at the same time.
Meeting that obviously creepy guy is weird and intense for her, the cinematography and music in the first episodes is really good, artsy and fitting the entire mood it wants to transport.
So while we find out the very first episode that the creepy looking guy is indeed a creep and crazy serial killer for that, we undertand that somehow he likes our female lead too and does not intend to kill her (or at least most of the time I guess).

So the pictures, the tension and the music are really well done in the first few episodes. The side characters are - ok.
The shaman friend seems interesting but her story isn't well explored, sadly she remains pale because that lack of background.
The other friend of our progammer lady is a female detective who, after an accident, is wheelchair bound.

Our serial killer seeks the cop lady out specifically on the chat bot luring her in with pretending he is in a wheel chair too. (how he is able to do that we don't know) For some unknown reason he does not kill her though, but leaves her out in the wild without her wheelchair. I did wonder though why did he not kill her as she could have easiyl intentified him? Also, why did she not check the police records for his face she being a police woman?

By the middle of the show it gets all rather slow and several things that happen seemed forced and incoherent to me and I started feeling a little annoyed.

It seemed like the creators wanted to put certain things into the story no matter what and how.
So the shaman woman is into women and it seems kind of forced that they almost artificially create a situation for her to meet a woman and get it going with her. No problem with that if it fits the story and you feel a connection to the character. That chance was missed in my opinion and so it just seems like they wanted this to somehow happen in that show.

Same thing goes for the handicapped cop lady. So she is a cop but although being in a wheelchair and thus comparably helpless she goes to a blind date with an unknown guy she just talked to per chat for a bit, and she doesn't meet him in public but is gullibly being lured into the wild to a forsaken swimmingpool sowewhere in the great nowhere? Would a cop, let alone a handicapped cop do such dumb thing really?

So then you have to just accept that quite accidentally, in a multi million city like Seoul, the serial killer gets involved with programmer girl and at the same time with her disabled cop friend. Not enough accidental things, he is even able to orchestrate a kind of rape game in a vacant industry hall at night, where programmer girl unknowingly meets a group of men who where made to believe she is meeting them for that rape role play. She doesn't know of course and despite being a very petite, untrained small woman she is not only able to escape all of them (unlikely) but even kills one of the with just one strike of a razor blade (very unlikely).
Meanwhile Mr. serial killer goes on killing while the police... hm, well it seems he can just go around killing in Seoul, the CCTV extreme city, and not only not being caught, but not even being sought after. (very, very unlikely).

it starts on dragging then, feeling like the creators couldn't decided what to do with the characters.
All of a sudden our autistic programmer girl is obsessively in love with the serial killer, but we don't really get to know why that happens all of a sudden.
The handicapped cop lad is out for revenge and instead of this time being wiser and getting backup when she wants to confront the serial killer, she - again - is dumb enough to be lured to a remote place, this time a whole vacant housing estate that is about to be demolished when she is there. And she really goes there alone again, with her wheelchair, into uneven demolishing ground, where this time she almost dies and is just being rescued the very last second. That was when I was annoyed because I thought how could someone with the police be that idiotic two times in a row? How did she even get to the police with that lack of intelligence in the first place?

Anyways, it then gets more artsy and abysmal, serial killer killing, programmer girl acting like a 12-year old obsessively in love with him ignoring all sensibility, and in the end deciding to kill the killer. That, sadly, wasn't done in any realistic way.
She still just has that small razor blade, and with it is able to make a slash through one eyeball, the nose including bone and the other eyeball. For this she would have neede something else, a mere small razor blade is not able to do that. But again, the creators wanted that effect of cut eyeballs, physics out the window. And again, no police while in a few weeks there are brutally murdered people everwhere and programmer girl happily celebrated with her friends.

Conclusion:

I did not know this was an adaption of a book and I do not know that book so I can't say if the adaption went well or not.
As mentioned in the beginning, this was promising and it could have been rather good, but somewhere in the middle the creators somehow lost their own plot. it got more and more confusing and the characters acting unlogical or plain dumb.

Creating a good storyline with this content is probably comparably difficult, but the downward tendency was just too steep for me from the middle of the show.