The first part of planned trilogy.
Filming take place in Daejeon, Cheongju, Busan, Wanju, Incheon, Gimje, Gunsan, Anshan & Paju.
Korean-Chinese murder contractors, expressed in Yanbian, enter South Korea and commit murder, and the original setting of these characters is said to have been soldiers who escaped from North Korea.
The clouds in the scene where Lee Joong-gu came out smoking the last cigarette were not CG, but real clouds.