Hà My, Minh Hằng, is an obese phone-sex part-timer and a ghost singer for Ammy, a famous pop star who lip-syncs her songs instead of singing live. Hà My harbors a crush on director Sang-jun Han, whose arrogant father Choi Han owns the record label Ammy is signed to. One day, Ammy sends Hà My an outfit supposedly from Sang-jun to wear to his birthday party, and Hà My wears the same outfit there to humiliate her. While crying in the restroom, Hà My overhears Sang-jun tell Ammy to be nice to her in order to keep using her voice. Heartbroken, Hà My attempts suicide but is interrupted by a phone call from one of her phone-sex clients, plastic surgeon Kong-hak Lee, who persuades her to undergo extensive plastic surgery.
After a year of seclusion while recovering from the surgery, Hà My becomes incredibly beautiful and slender, so much so that even her best friend Jung-min Park cannot recognize her at first. With Jung-min's help, Hà My reinvents herself as a Korean-American from California named Jenny. After re-auditioning to be Ammy's secret vocalist, she earns her own recording contract. Meanwhile, Ammy fears her own inability to sing will be exposed if the release of her second album is delayed. She desperately tries to find Hanna by spending time with Hanna's father, who is suffering from Alzheimer's, but Sang-jun orders her to give up, threatening to terminate her contract if she does not.
After many encounters with Jenny, the truth slowly comes to light: Jenny is, in fact, Hanna.
Jenny's debut single “Maria” becomes a hit, and at the release party Ammy brings Hanna's father in an attempt to blow her cover. Desperate to keep her true identity a secret, Hanna ignores her father, infuriating Jung-min with her indifference. After the party, Sang-jun tells Hanna that he knows who she is and cannot forgive her for lying. Hanna confesses her love for him and reveals that she underwent plastic surgery to make him love her back. After realizing how little she meant to him even as Jenny, Hanna decides that she is better off without him.
The next day, Ammy threatens to reveal Hanna's deception unless Sang-jun cancels Hanna's concert. Though Choi agrees, Sang-jun stands up to them and refuses, encouraging Hanna to perform the concert for herself, not for fans or the label. Before taking the stage, Hanna apologizes to Jung-min for her earlier behavior, though Jung-min rebukes Hanna for the way she treated her own father. At the concert, Hanna tearfully confesses to the audience that she was a ghost singer while she was overweight and had extensive plastic surgery, and that she abandoned everything dear to her—her best friend and her father—for her career. Sang-jun plays a tape of the old, overweight Hanna singing, which Hanna says is the real her. The crowd is moved by her honesty and praises her for showing her true self. Hanna reconciles with her father and Jung-min, drops the stage-name Jenny, and becomes a highly successful music artist in her own name. Sang-jun realizes that he has always been in love with Hanna and continues to promote her in the hope of pursuing a relationship.
