I so enjoyed this action packed, intriguing and very amusing caper.
It is not perfect, but, it got a 9 from me purely for how much I enjoyed every episode; I totally binge watched it.
I did work out the key aspect fairly on, but was still gripped all the way through.
Loved Soo-yeol (LDW) and how, whilst a pretty sycophantic and underhand detective in (perversely) the Anti Corruption Unit, he still had a conscience and couldn't turn a complete blind eye to certain crimes (especially once influenced by K).
K (perfectly played by Wi Ha-joon) was stunning ~ like OTT, action hero stunning ~ and that fits totally (especially as the story unfolds).
Character, Hee-kyum, is feisty, by-the-book and very capable of handling herself; but she was also often too headstrong and didn't listen, which irritated me.
Rookie Kyung-tae, was a total sweetie, stuck by his guns and refused to ignore the signs that all was not as it should be, with the investigation and conclusion of a certain serious crime. This put him in danger, but he never gave up.
Ji-ru (Soo-yeol's boss) was actually very supportive, considering SY's previously compliant attitude to do what he was ordered, changed pretty drastically.
There is a lot of violence and some very uncomfortable scenes, but there's also wit, sarcasm and "that could never happen" scenarios, which still fit nevertheless!
This isn't 'real', isn't to be taken too seriously and needs a certain amount of imagination (because it's hard to portray the subject of this drama ~ which you'll know what I mean if you watch it), but it really is terrific fun and very touching on several occasions. Loved it.