Seoul is ravaged by the “Beast Plague,” a disaster that transforms humans into monsters. Lir, a boy with sharp instincts, struggles to survive while caring for his sick younger sibling. One day, a mysterious incident occurs at the hospital. In a desperate attempt to protect his only family, Lir awakens on the thin line between human and beast. “I promise you—I’ll get you back, no matter what.” “Even if I have to become a beast to do it.”