In a world where monster hunters are hailed as heroes, Cheon Haesun has been treated like an outcast because of his abnormal looks. As if that wasn't bad enough, a pack of monsters attacks his neighborhood on the day he discovers he's dying from an unknown illness! With his sister's sacrifice, Haesun survives and somehow awakens to become a Poisoner, a rare hunter with toxic healing abilities. But will his poisonous powers cure Haesun's illness and guarantee a normal life he's always dreamed of?