Hellbound takes place in 2022–27 in South Korea. An otherworldly face called an angel suddenly starts to materialize to deliver prophecies called decrees that condemn certain individuals to Hell at a specific future time, either seconds or years away. Three monstrous supernatural beings called demons appear at almost the exact time to maul and incinerate the person's body in a spectacular show of force called a demonstration. Two organizations in cahoots, the cult-like New Truth Society and the gang-like Arrowhead group, gain power by playing on people's fears.

Professor Se-jeong is thrust into a bloody nightmare when a rapidly mutating virus is released during a biotech conference causing authorities to seal the facility. Trapped inside with no escape, Se-jeong along with a small group of survivors must fight to stay alive while the infected undergo horrific transformations.