Let's start this pretty long review by saying that this drama made a rookie actor shine like a veteran. We all know that OCN is amazing when it comes to Chasing and thriller drama (Voice and Tunnel were gems). Duel plot centers around a group of people who are obsessed with a vaccine that might cure terminal illness. We have different characters, all of them are connected to each other somehow: two clones seeking for a way to survive. One is taking revenge on those bad guys who treated him like an animal, the other one is trying to help a veteran cop to find his kidnapped daughter. This drama started really well, the plot was thrilling, the characters were well scripted. But, sadly, toward the end it started to be a little bit sloppy and the plot has some black holes. First of all, let me talk about the two twins. SungJoon is the nice guy. He was used by his twin as an escapegot, when he committed some homicides he blamed them all to his twin. He has no memories at first, he doesn't know who he was and why there's a guy who looks exactly like him without being his twin by blood. His character's psychology is not bad. He's too kind, too soft and too innocent to be the real villain. In fact, the drama didn't give us any suspense. We know that there won't be any plot twists about him right in the first episodes of this drama. Pretty disappointing, though. The real gem of this drama is SungHoon. Evil, clever and with some guts. He seeks revenge, he seeks life and he's doing everything to achieve these two things. He was a victim too, yet no one gave a damn about him. Reason to watch it : SungHoon, obviously. We can see his character grow during the drama. Reason to not watch it: Mirae and the bloody sick kid were useless. Both annoying characters, they didn't make the audience sympathize with them. The way the police handle the case of Sunghoon left me speechless. When they found out who he was and why he was doing all those bad things they even tried to help him out neither for a tiny second. If you are watching this to see some sweet moments between the two twins, drop it. Sunghoon isn't a sweet guy. All the bad things that had happened to him turned him into someone who is just filled with anger and grudge. He doesn't forgive his brother for not trying to find him and even in the end, even though we can see a little bit of change in his mind, I couldn't see a real affection for his twin. Yup, he did try to save SungJoon in the end, yet I still didn't see that love that brothers share. SungJoon loved his twin. But, let's be honest here.... Did he really try to help him out? He was all into saving that annoying kid that, in the end, I started to find him a pain in the ass. IS THE ENDING WORTH THE WATCH? No, if we are only talking about the ending... Absolutely not. Korean dramas are predictable, we all know it. It doesn't give justice to any of its characters and it left me with some sour taste on my tongue. IS THERE ANY ROMANCE? Nope, thank's God there isn't any romantic story between the characters. They tried to pair up SungJoon with Mirae, but romance were useless in this plot and thank's God the screenwriters knew it before screwing up everything. I secretly ship SungHoon with SeoJin though. IS THERE ANY SUSPANCE? I might say no... After 5 episodes you know exactly how is going to end. These drama could have been perfect if they tried to focus a little more on the twins background story and their relationship. IN THE END, DID I LIKE IT? I might say so. SeJong is amazing, he made me his fan right after the first episode. I'll give this drama 6.5 out of 10 because the ending ruined EVERYTHING.