First of all, the cast is extraordinary!
Lee Dong-Wook as Ryu Sool-yeol is the protagonist, but accompanied by his hero sidekick, Wi Ha-joon (as K, his alter ego). The two of them create one of the most fun and unusual bromances in film!
But the rest of the cast is just as stellar, with Jung Sung Il as the villain you love to hate, and Kim Hieora as Boss Yoon, the villainess you cheer for, at least at the end.
Han Ji-eun is also great as the super cool detective/ love interest, and it's especially fun when K gets involved.
N (Cha Hak Yeon) is Oh Kyeong-tae, another great performance in the world of detectives.
A really enjoyable watch; I'm hoping for another season!