In a world where doppelgängers exist and are tasked with killing their human counterparts, a devil named Joon falls prey to distraction and accidentally creates Doh Seong-ah. He's supposed to be taking the place of Lee Woo-yeol, but instead comes out looking like the male version of Joon's favorite idol! Undeterred, Seong-ah enters the human realm to start his mission, but Woo-yeol proves to be far more formidable and terrifying than Seong-ah anticipated... Can he succeed in eliminating Woo-yeol? Or will the world be big enough for the two of them after all...?