Hanna Kang is an overweight phone sex part-timer and a ghost singer for Ammy, a famous pop singer who actually lip syncs. Instead of being famous for her own amazing vocal talent, Han-na sings backstage during Ammy's performance and Ammy takes all the credit, while Han-na records all of Ammy's songs. Other than that, Hanna has a huge crush for Sang-jun who's a director and his arrogant father owns the entertainment company. One day, Ammy purposely insults Hanna's weight in front of Sang-jun during his birthday party, knowing well that Han-na likes him. While crying in the bathroom, Hanna overhears Sang-jun telling Ammy that even though they are just using Hanna for her voice, they must be kind to her so she will not walk out on them. Heartbroken, Hanna attempts suicide with a gas leak but is interrupted by a phone call from one of her phone sex regulars who happens to be a top plastic surgeon. She asks him to perform a head-to-toe plastic surgery operation on her, for which she'll pay him back later on, but he denies her request. She then tries to blackmail him with recorded tapes and destroys them in front of him to convince him about the depth of her insecurity and pain in being fat. The surgeon refuses to operate further on Hanna, but Hanna threatens to inform his wife about his secret fascination. Then, Hanna 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 vote of confidence so that she can live a happy life, and the surgeon is deeply moved in the end. Hanna puts herself in seclusion for a year as she recovers from the changes from the surgery and weight loss.When she comes back from the hospital, Hanna is incredibly beautiful and slender. Not even her best friend Jung-min recognizes her until a trip to the bathroom shows she still has her back tattoo. At a restaurant, Hanna is made aware that Ammy blames her for making her postpone the recording of her 2nd album and that she was forced to do a sitcom show. With Jung-min's help, Hanna 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 Hanna's new identity, is afraid of a possible competition with Jenny for album sales and desperately tries to find Han-na so that she can record her own postponed album (since she can't sing the songs herself) by spending time with Han-na's father who is in a hospital due to mental problems, possibly Alzheimer's. She hopes that in spending time with him, he can help her find Han-na so she can convince her to come back and help record her 2nd album. While in the bathroom, Ammy gets a call from Sang-jun who tells her that he isn't pleased with her attempts to find her ghost singer so she can finish her postponed 2nd album. He orders Ammy to give up her search for Hanna and give Jenny a chance to help her finish her album. He already had given up searching for Hanna and wants her to do the same. Sang-jun also orders Ammy to focus on memorizing her lines for a show(that he got her in much to her detest) or she'll lose her job. Disgusted with the reminder of memorizing her lines for the sitcom and being threatened with losing her job, Ammy tells him that she'll find Hanna because like a dog, she'll come running back to her. Meanwhile, romance begins to blossom between Jenny and Sang-jun, as he continues to promote Jenny, in effect boosting Hanna's confidence in her new self. However, after spending time with Han-na's father and Jenny, Ammy eventually realizes that Jenny is actually Hanna in disguise. She begins her attack on Hanna right away in an attempt at revenge for making her postpone the release of her 2nd album.During a date one night, Jenny refuses Sang-jun's advances, as the surgeon mentions that if he touches her breasts, he will immediately know they are fake. She instead offers a phone sex session. After Jenny has fallen asleep, he sees the African character Jenny had drawn on the glass and realizes that he had seen it before; Hanna had drawn exactly the same signs on a sheet of music. He then realizes as well that Jenny is actually Hanna, 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 the party however, Ammy brings Han-a's father in an attempt to blow her cover. Hanna's father tries to return Hanna's Barbie doll to her, which had always been Han-na's favorite 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, Hanna 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 insisting on giving her the doll, Sang-jun drags him away from Jenny and knocks him down onto the floor. Desperate to keep her true identity a secret, Hanna makes no move to help her father. It is Jung-min who finally helps him up, casts Jenny a furious look and leads Hanna's father away from the party.After the party, Sang-jun and Jenny are 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 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. Hanna breaks down at this point, heartbroken and unable to pretend to be someone else anymore. She tears down the posters and smashes her CDs that are placed on a table and got cut from the CDs. Hanna tells him that it is incredibly frustrating and painful not being able to 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 realizing that she still could not be close to Sang-jun. Hanna also makes the point across that even as Jenny, she always felt like she was worthless to him and he cared more about himself than her. As Sang-jun tries to comfort her, she brushes away his efforts saying, "You broke my heart. Tissue paper cannot fix it." Hanna visits the surgeon at his office and he tries to console her by mentioning that Sang-jun wasn't worth her grief. With her newfound beauty, he is confident that she would find someone else. Hanna asks the to come to the concert anyway as the ticket was expensive, but also complimentary. The truth eventually reaches the company boss and he is disappointed with the whole thing after being secretly sent side by side photos of Hanna and Jenny.During the meeting before the concert, Sang-jun apologizes and takes responsibility for the deception in not telling his father the truth about Jenny's real identity being Hanna. Despite being warned to cancel the concert, he insists on going through with the concert after reminding the boss that he was the one who helped the company and proves his point by smashing a small bourbon glass cup, while getting a cut on his hand. Later, Sang-jun encourages a distraught Ha-na to do this concert, not for the sake of the fans or the company but for herself, thus implying that he has forgiven her and will continue to support her. When Hanna asked what he would do with Ammy as she would plan to use the concert to embarrass her further, he replied he took care of it. Sang-jun admitted he knew Ammy was behind it and had her fired after what she did to embarrass Hanna. At the concert, Jenny can't sing and later breaks down from the pressure of seeing her father being dragged away by security and tells everybody to stop. She then reveals to the public that Jenny is a "fake," and that she is not "all-natural", as she had claimed. Hanna proceeds tearfully to tell the large crowd her story: that she was a ghost singer to an ungrateful Ammy while she was overweight, how she went into a year of seclusion to heal from the changes from the surgery and that she has abandoned everything that is dear to her, including her best friend and father, to get to where she is. She also tells the crowd about how on the way to fame and fortune she has also lost her own identity and that she can no longer continue singing under Jenny anymore. Sang-jun plays a tape of the old, obese Hanna, singing. Han-na turns around and sees her old image on the screen and tells the crowd that the image is the real her. The crowd, moved by her sincere confession, responds by chanting "It's okay". Hanna 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 fans and anti-fans along the way. Sang-jun realizes the very thing about Hanna that had always drawn him to her was Hanna's innocence, and continues to promote her. There is even a hint that there are again feelings blossoming. Who knows what will happen in the future...During the post credits, Jung-min also asks to get a head-to-toe plastic surgery from the surgeon.
Output: Question: What does Hanna threaten the surgeon with?, Answer: that she will reveal Jenny`s deception if the concert was not cancelled