Do Do-hee is the successor to the Future Group. She has an arrogant and cold-blooded personality, is cynical about love and has no faith in anyone. She comes into contact with Jeong Gu-won, a demon who has been living as a predator for 200 years. He can live forever by making dangerous deals with people who live hellish lives. When Do-hee saves his life, Gu-won loses his powers and must stay close to her to prevent himself from dying out. While she experiences major changes in her life, a romantic relationship develops.