The Devil Kdrama Plot/Storyline When the door to another world opens, demons are there. Ku San-Young (Kim Tae-Ri) has one of these demons. Yeom Hae-Sang (Oh Jung-Se) can see the demon possessing Ku San-Young. They are trying to find out the true cause of the mysterious deaths associated with the five holy things. Ku San-Young worked time working days and studied during a business period without notice at night. One day, he delivers some topics from his father early. Since then, a mysterious death has been happening around him. And he finds himself slowly changing. Yeom Hae-Sang comes from a wealthy background. He teaches Korean mythology at the university. Since he was a child, he has had a special ability to see demons in this world. He also saw the demon that killed his mother in front of him when he was a child. Yeom Hae-Sang meets Ku San-Young and he confronts the demon that killed his mother. Lee Hong-Sae (Hong Kyung) is the head of a violent crime investigation team. He is only thinking about improving his career in the police department. Because of Ku San-Young and Yeom Hae-Sang, he is involved in a mysterious business.