In the infernal depths of hell, Cain, a devil longing to return to Heaven with his brother Abel, forges sinister contracts with mortals. But his world is shattered when Abel is murdered by Yeonli, his own contractee. To make things worse, Yeonli then shoots Cain with a cursed "golden bullet of love," igniting an agonizing battle within him. Despite his seething hatred, he's entrapped by uncontrollable love and lust for her. Now, Cain must navigate a treacherous path, seeking revenge on his brother's murderer while suppressing his intense desire. Will Cain conquer the bullet's spell before Yeonli reaps his soul too?