Kang Han-na (Kim Ah-jung) is an overweight phone sex employee and a secret vocalist for Ammy, a famous Korean pop singer who actually lip syncs as she cannot sing. Instead of being famous for her own amazing vocal talent, Han-na hides behind Ammy's performance stage and sings during Ammy's concerts, and records all of Ammy's songs. One day, Ammy ungratefully humiliates her in front of the music company's director Sang-jun (Ju Jin-mo) during his birthday party, knowing full well that Han-na has a crush on him. While crying in the bathroom, Han-na overhears Sang-jun telling Ammy that even though they are just using Han-na for her voice, they must be kind to her so she will not walk out on them. Heartbroken, Han-na attempts suicide but is interrupted by a phone call from one of her phone sex regulars who happens to be a top cosmetic surgeon. She decides to get a head-to-toe makeover instead. The surgeon at first refuses to operate on Han-na, but Han-na blackmails that she will tell the surgeon's wife about his calls. Then, Han-na makes a moving speech that she does not want to undergo surgery merely to be beautiful, but for the sake of love and as a boost in confidence, and the surgeon is deeply moved. Han-na puts herself in seclusion for a year as she recovers from the changes.

When she comes back from the hospital, Han-na is incredibly beautiful and slender. No one, not even her best friend, Chung-min, recognizes her. With Chung-min's help, she creates a new identity for herself; she is now a Korean-American from California named Jenny. After auditioning to be Ammy's secret vocalist again, she earns her own recording contract instead from Sang-jun, claiming that she is "all-natural". In the meantime, Ammy, oblivious just like everyone else of Han-na's new identity, desperately tries to find Han-na so that she can record her own postponed album (since she cannot sing the songs herself) by spending time with Hanna's father who is in a hospital with some mental problems, possibly Alzheimer's. Through spending time with Han-na's father, she eventually realizes that this new Jenny is actually Han-na in disguise. Meanwhile, romance begins to blossom between "Jenny" and Sang-Jun. During a date one night, as sparks fly, Jenny supposedly stripped for Sang-Jun in the character of a nurse [not shown on camera, of course] After Jenny has fallen asleep, he realizes that the tattoo Jenny had on her hip was a sign he had seen before. He remembers that when Han-na still existed and he had not met "Jenny" yet, Han-na had drawn the exact same signs on a sheet of music. Then he adds all of the signs up and realizes as well that "Jenny" is actually Kang Han-na but he keeps this information to himself.

"Jenny's" debut single 'Maria' becomes a hit and the recording company holds a party to celebrate its release. On the day of a party however, Ammy brings "Jenny's" father, in an attempt to blow Han-na's cover. Han-na's father tries to return Han-na's Barbie doll to her, which has always been Han-na's favourite childhood gift from him. Startled by the sudden appearance of her father and not knowing how to react in front of all the people, including Sang-jun, Han-na denies knowing her father and calls him a fan instead when Sang-jun asks her if the old man is her guest. As her father keeps on insisting on giving the doll to Han-na, Sang-jun drags him away from Jenny and accidentally knocks him down onto the floor. Desperate to keep her true identity a secret, Han-na made no move to help her father. It was Chung-min who finally helps him up and leads him away from the party.

After the party, Sang-jun and 'Jenny' were the only ones left in the room. Sang-jun reveals to 'Jenny' that he knows her true identity but is now cold and distant. He seems to be unable to forgive her for lying to him but says that he will still work to promote 'Jenny' and carry on with her concert scheduled the next day. Han-na breaks down at this point, heartbroken and unable to pretend to be someone else anymore. Han-na tells him that it is incredibly frustrating and painful not being able to be just be herself but have to live a lie, especially in front of him. The surgery that took a whole year to recover from was not nearly as painful as realising that she still could not be close to Sang-jun.

The day of "Jenny's" first concert, Jenny breaks down from the pressure of losing her friend and father and reveals to the public that Jenny is a "fake," and that she is not "all-natural", as she had claimed, but is "plastic". However, nobody seems to believe her. She proceeds tearfully to tell the large crowd her story: how she has abandoned everything that is dear to her - her best friend and father - to get to where she is. She also tells the crowd about how along the way to fame and fortune she has also lost her own identity and that she now no longer knows who she is. Just then, the screens behind her on the stage started to show a clip of the old, obese Han-na, singing angelically. Han-na turns around and sees her old image and tells the crowd that the image is the real her. The crowd, moved by her sincere confession, responds by chanting "It's okay," and Han-na rekindles her relationships with her father and best friend. She drops the stage name "Jenny" and re-releases a CD with her own name, Hanna, and becomes a highly successful music artist, gaining many anti-fans as well as loyal fans along the way. Sang-jun realizes the very thing about Han-na that had always drawn her to him - Han-na's innocence.