Episode 15 starts with Na Ok-hui striking Mi-jin from behind. Fortunately, Mi-jin had contacted Da-young about her predicament and requested her to alert the authorities.
Da-young lets Byung-duk know, who then informs Ji-ung. Ji-ung and Byung-duk reach the place given by Mi-jin to Da-young, but only discover her phone and father, with no sight of Ok-hui or Mi-jin. This is the moment when one of the officers discloses that Na Ok-hui owns a historic house nearby, and they start making their way towards the property.
At the same time, Mi-jin awakens to find herself tied up while Na Ok-hui gets ready to end her life. Nonetheless, with Na Ok-hui appearing to be intoxicated, it provides Mi-jin an opportunity to utilize the blade concealed in her pocket, free herself, and escape with the killer close behind.
Police, Ji-ung, and Byung-duk reach Na Ok-hui’s residence, only to discover it empty. Ji-ung anxiously looks around the property and locates the dilapidated shed with evidence of blood. He proceeds to accompany them into the wilderness in search of Mi-jin and Na Ok-hui.
Meanwhile, Na Ok-hui nearly causes Mi-jin’s death but hesitates when she sees a vision of her aunt. Mi-jin has sufficient time to inject the fentanyl-filled syringe into Na Ok-hui’s leg, secure the leg, and depart. Ji-ung discovers Na Ok-hui restrained and requests for additional support.
He comes across Mi-jin’s enigmatic cat, leading him to a wounded Mi-jin approaching him, but as the sun comes up, Mi-jin loses consciousness and transforms into Lim Sun.
Then, she discovers that she is in the hospital. Her father had been saved as well. In another location, Ji-ung and his group discover skeletons buried in Na Ok-hui’s yard, which they determine to be Ji-ung’s mother and Mi-jin’s aunt. After the sun sets, Mi-jin reverts to her original self and reunites with her family, at which point her mother learns about her sister’s remains as well.
When questioned in the interrogation room, it is discovered that Ji-ung’s mother was employed at Ms. Kwak’s, where Na Ok-hui had either worked before or joined later, following the incident where the woman witnessed her killing Lim Sun. Luckily for her, Ji-ung’s mother believed the killer was a male.
While waiting for the detective to arrive, Na Ok-hui murdered her. Before passing away, she had pleaded to be saved for her son’s sake, showing that she truly cared for Ji-ung.
Mi-jin, disguised as Lim Sun, tells Baek Cheol-gyu about Na Ok-hui’s detention while he’s behind bars. Later, prosecutor Cheon-hui points out that Lim Sun and Ko Won’s statements are too perfectly aligned. In the meantime, Mi-jin has been attempting to steer clear of Ji-ung. Once Mi-jin departs from Da-young’s home in the evening, Da-young meets with Byung Duk who just drove in and tells him to stop flirting with her because she doesn’t do married men. She is shocked when Byung-duk tells her he is single and that he had a complicated situation. Da young then asks him to join her for ramen.
In the meantime, Mi-jin returns to her house and discovers Ji-ung waiting for her. She tells him the truth about herself even though Ji-ung is aware of her secret and requests to part ways because she doesn’t want to endanger him as he was instrumental in resolving her case discreetly.
The following day, we find out that Cheon-hui had found out that Lim Sun had lied about her identity to get a job at the prosecutor’s office. Cheon-hui informs the Chief, who chooses not to take action because Ji-ung had threatened to damage the office’s reputation by exposing that they had been tricked twice. We also discover that he will depart for Seoul in the near future.
Back at Mi-jin’s residence, Mi-jin’s mother is surprised to learn about her sister’s passing and opts to meet with Ji-ung. Lim Sun, portrayed by Mi-jin, attempts to prevent her. Lim Sun’s mother sees her as her missing sister but is surprised when Lim Sun transforms into Mi-jin every evening at sunset in front of them.
Episode 16 starts with Mi-jin’s parents uncovering her unique condition – her body changes into Lim Sun during the day but returns to Mi-jin at night. They make an effort to uplift her spirits by offering skin care products to minimize signs of aging. At the same time, Baek Cheol-gyu receives a shortened sentence for working with the police and at the request of Mi-jin for mercy.
Mi-jin does not revert to her previous self even after the case is over. She takes control of her situation by signing up for a gym to combat aging, getting insurance, and preparing her parents for independent living in case she’s not around. It’s like she has started to truly experience life, traveling with her parents and spending time with Da-young, fully conscious of life’s fleeting nature and recognizing that her youth was a precious present. In these moments, she reflects on her time working at the prosecutors’ office and ultimately finds her true passion in life.
This time, Mi-jin is getting ready for the civil services exams again, not to fulfill her mother’s dream but for her own sake.
At the same time, we discover that Ji-ung has been moved back to the Seoul branch, and he pays a final visit to Mi-jin’s parents. Her father attempts to delay Mi-jin’s return so that Ji-ung can stay longer, but in the end he has to allow Ji-ung to leave. It was later discovered that Mi-jin had spotted Ji-ung in front of her house and chose to avoid him until he had departed.
Afterwards, Byeong-duk nearly falls for another scam when attempting to purchase a used ring for Da-young, but luckily, Ji-ung is there to keep an eye on him and the scammer. This is also the moment when Ji-ung says farewell to Byeong-duk despite enduring his disapproval of his transfer. In another location, Mi-jin, spending time with Da-young, notices a cat that looks familiar to Lim Sun, but doesn’t give it much thought. During her dream, Mi-jin is visited by her older self Lim Sun, who says a final farewell to her. And right on cue, Mi-jin returns to her usual self.
The following day, after many months, Mi-jin finally acts like herself during the day and testifies against the fake Na Ok-hui at court, asking for a harsh punishment. On judgment day, Mi-jin discovers that Ji-ung is returning to Seoul while the culprit is sentenced to death for the atrocious acts she carried out. Afterwards that evening, Mi-jin’s family rejoices over their triumph in the trial while Ji-ung discreetly returns Mi-jin’s cactus that she had taken care of while they were working together.
As time goes on, Ko Won comes back as a pop star and launches a hit song influenced by his experiences with Mi-jin. During a flashback, Ko Won and Mi-jin converse, with Mi-jin expressing gratitude for their friendship but also mentioning that her relationship with Ji-ung is not over. Da-young and Byung-duk become engaged to each other..
Half a year later, Ji-ung returns to the Seoul office for lunch with his coworker and encounters Mi-jin, the office’s fresh top investigator. Despite her colleague’s interest, Ji-ung successfully wins back her love as they reignite their relationship and progress towards a happy ending.
Miss Night and Day has ended typing up its loose ends. Although the series started off well, it didn’t quite live up to its potential. It’s good but forgettable. Anyway, what do you all think about this series?