Responses

Yes, I believe that it's based on a novel since the adaptation said so. The title of the drama is Walking In The Dark, this is the link ( https://mydramalist.com/64465-in-the-dark)!
I also can't wait for everything to be revealed since I'm also damn confused and tmi
You're welcome!!!
Aight so I feel you when y'all said that it's confusing. I just wanna share my explanation about Xie Lanshang (and not the case they're investigating cuz I'm still confused lmao). Also thanks to ( https://mydramalist.com/64465-in-the-dark) for the synopsis of the drama adaptation on 2021!
Xie Lanshan is a police officer and an undercover. In the drowning scene during his mission, he literally DIED. Yes. Sui Gong (captain of the drug trade police force; which I believe wasn't introduced yet) transferred the memories of the original XLS which is dead, to the death row criminal who LOOKS EXACTLY LIKE HIM. That explains why he had a personality change (see first few chapters). Then, the memories of the CRIMINAL are slowly returning to him (XLS in the criminal's body) since y'all know about the memory transfer, right? Wherein the original owner of the body's memories were overpowered (I forgot the exact word) by the memories transferred.
Fun fact: According to the drama synopsis, Mu Kun (the leader of the drug org. where XLS undercovered) is the FATHER of the death row criminal (aka XLS's present body).
Now, with Shen Liufei. I believe that the XLS he knows is the criminal one, and not the real XLS (deceased). I'm guessing the the criminal had a long hair which were then cut into the real XLS's hair style.
That's all (●'◡'●)ノ