Top star Momo falls into a coma after an unexpected accident. Her mother, Ran-hee, proposes a shocking solution to Momo's lover, neurosurgeon Ju-shin, to transfer Momo's soul into her own body through a brain transplant. Although it is a dangerous gamble, Ju-shin makes the fateful decision to perform the surgery.

Six months before Momo's accident, Yong-joong learns that Ba-ra is the child he met 16 years ago. Meanwhile, Ju-shin pressures Momo to marry him. Although she resists, Ju-shin sends expensive pieces of jewelry and promises to take responsibility, leaving Momo increasingly torn despite her mother's strong opposition.

Momo goes missing after a scuba diving accident. Ba-ra, a journalist, senses something suspicious about the case, while Yong-joong also feels an unsettling vibe from Ju-shin. Meanwhile, Ba-ra reveals the engagement of Ju-shin and Momo in an exclusive interview without informing him, as Momo calls 911 to report her mother's death.

Ran-hee's lifeless body is taken away, and Ju-shin mourns for Momo. The funeral proceeds, but those around her cannot believe she would take her own life with no apparent reason. Meanwhile, Momo, who now carries Ran-hee's soul, pretends to mourn while contemplating the possibilities of her new life.

Ju-shin begins to feel a growing sense of unease toward Ran-hee, who now has Momo's appearance. Over a meal with Jin-ju, Ju-shin tries to gauge her feelings. Meanwhile, Yong-joong confesses his feelings to Ba-ra, and Ba-ra begins to see hallucinations of Momo.

Ran-hee grows increasingly irritable as she tries to get closer to Ju-shin. However, Ju-shin seeks out Jin-ju, shows interest in her, and urges her to undergo the surgery. After meeting Gwang-cheol, her supposed biological father, Jin-ju vanishes without a trace, leaving behind only a single letter that shocks everyone.

Ju-shin successfully transplants Jin-ju into Momo's body. As she begins life as Momo, her biological father searches for her, waiting and refusing to believe she's dead. Meanwhile, Jin-ju offers Ba-ra a job to work by her side, and Ju-shin grows drawn to Ba-ra as he senses something is off with Jin-ju.

As Ju-shin looks deeper into Ba-ra, he finds himself increasingly drawn to her and even makes her an unthinkable offer. Ba-ra accepts Momo's proposal, quitting her job to stay by her side, while Jin-ju's father continues his relentless search for her. Meanwhile, Jin-ju, as Momo, discovers she's pregnant and hesitantly confides in Ju-shin.

Jin-ju seeks revenge on Ba-ra and tries to seduce Yong-joong while in Momo's body. Meanwhile, Gwang-cheol continues to appear before Jin-ju, who now inhabits Momo's body, pressuring her at every turn. Amid it all, Ju-shin and Ba-ra find themselves drawn into a tense, ambiguous moment as they head into the bedroom together.

As Jin-ju reels from Gwang-cheol's shocking visit, she cuts ties with Ju-shin and turns to Yong-joong, with whom she shares a past. She urges him for his full support, and they go to a karaoke room for drinks. Meanwhile, certain of his feelings, Ju-shin shocks Ba-ra with a marriage proposal.

Yong-joong warns Ba-ra to keep her distance from Ju-shin, but the two only grow closer. As Ju-shin continues to pursue Ba-ra, Jin-ju learns that Ju-shin had proposed to Ba-ra and gets overcome with fury. Suddenly, panic overcomes Ju-shin as he learns that Ba-ra is secretly planning to go away.

Yong-joong tells Ba-ra they should set a wedding date, but Ba-ra leaves him and heads to Ju-shin's house. Meanwhile, Gwang-cheol begins volunteering at Nua General Hospital, and Jin-ju is delighted when she hears something unexpected from Yong-joong.

Ba-ra is devastated to learn that Jin-ju is actually Momo and confronts her with a final plea. Despite this, Jin-ju and Yong-joong go through with their wedding. Meanwhile, Ju-shin asks Ba-ra if she would consider undergoing a brain change into Momo's body to be with Yong-joong.

Yong-joong and Ju-shin discover Ba-ra's pregnancy. After seeing Momo wearing Jin-ju's earrings, Gwang-cheol's suspicions deepen. At Paul-kim's house, Ba-ra stumbles on a picture that looks just like her. Meanwhile, Yong-joong and Momo's relationship hurtles toward an irreversible breakdown.

Cornered and desperate, Jin-ju tries to convince Ba-ra to undergo the brain swap. Meanwhile, Yong-joong promises Ba-ra eternal love, and Jin-ju begins to reveal the full truth behind the brain change to Gwang-cheol. Later, when Yong-joong visits Ba-ra at the hospital, he finds that she has disappeared.

Gwang-cheol is devastated by Jin-ju's death and, consumed by rage, confronts Ju-shin. As Yong-joong mourns Jin-ju, Paul Kim shocks James with news about his long-lost daughter. Meanwhile, Jin-ju appears at the funeral as a spirit, and a body is discovered at Nua Hospital.