Mo Du (link to English translation by E. Danglars) is very, very good. I kinda inhaled the five books in the series. It's just-- so good, it's hard to recommend because I'm so full of "!!!". Also, it's one of those series that's better the less spoiled you are, which makes it very hard to give pitches in the form of "And then [X] does [Y] and it's so good!!!!!"
The blurb is as such:
Childhood, upbringing, family background, social connections, traumas...
We ceaselessly seek and explore the motives of criminals, pursue every trace of the emotions driving them, not to sympathize with them and even forgive them, not to find a reason to exonerate them of their crimes, not to bow before the so-called complexities of human nature, not to reflect on social conflicts, and certainly not to become monsters ourselves—
We are simply looking for a just answer for ourselves—and for those who still have hope for this world.
Which definitely hits on the themes, but doesn't really describe what happens.
Mo Du is one part action-mystery and one part slow burn rivals-to-lovers. The mystery plot line is great. It's full of twists, but they all hit that balance between "wHAT?!" and "oh, that makes total sense! I should have guessed that!) The romance is also very good. It's a slow burn, but it doesn't feel like it's getting stretched out, because the mystery plot is filling in the spaces between that smouldering burn. The dynamics between the two leads, and how that dynamic evolves, is really good.
There's also an exploration of trauma, characters that Sure Do Have Some Backstories. Also, some very good hurt/comfort scenes.
Our two leads are Luo Wenzhou-- the morally upright, no-nonsense head of the Criminal Investigation team-- and Fei Du-- the mega rich son of a CEO, who is very good at saying exactly what people want and/or trolling them, and also keeps getting involved with investigations for unclear reasons. They bounce off each other so well. (Especially because Fei Du tends to troll Luo Wenzhou, instead of doing the 'saying what you want me to say' thing.)