The seemingly ordinary hardware manufacturing company is actually a cold and ruthless killing company like copper metal. Although Chi Hyung-do (played by So Ji-sub) is dressed in a suit all day, he is a professional killer with outstanding performance in the company. He has worked for the company for ten years without a single miss, and has long honed his cold-blooded temperament and ruthless killing. But when he met Luo Xun (played by Kim Dong-jun), a newcomer who came to the company to "work", he suddenly saw his shadow back then. When performing tasks with Luo Xun, Hyung-do had a moment of trance. Through communication with Luo Xun's family, he felt more and more the warmth of family affection, and when he met his beloved woman Liu Mi-yeon (played by Lee Mi-yeon), his professional sensitivity changed. When performing a mission, the mission failed due to hesitation, which also made Hyung-do have the idea of retreating for the first time, but things were far from as simple as he imagined. Within a day, he went from the most promising employee of the company to the enemy of the company, and was hunted down by his former colleagues as a "target"...