Hyun-jae, a 16-year-old escaping her abusive father, manipulates Hae-in, a woman searching for her missing daughter, into taking her in as a replacement. Over the summer, Hyun-jae bonds with Hae-in, finding peace through her love for singing, but becomes obsessed with becoming Hae-in's new daughter. When Hae-in learns her missing daughter may have been found, Hyun-jae, despite her fears, makes a selfless decision to accompany her, realizing she can't replace Yun-seul.