I'm not sure why, but I'm usually not into Korean dramas, but I find this drama to be a strangely good mix of comedy, thriller, mystery.

In her quest to solve the mystery behind her sister's disappearance, Yoo Ryung becomes a police officer and manages to get herself transferred to the subway police department because she believes that her sister has been the victim of the subway ghost, a serial killer who has killed people and dumped bodies in the subway.

Fueled by empathy for the victims and their families, she goes after criminals with a passion, turning the otherwise mundane world of the subway police department upside down. The comic situations are rather funny at the start. However, the series does not go light on the crimes: some of them can be rather violent, and the series does not hesitate to show some violent scenes.

I wasn't expecting it, but the blend of light-hearted comic elements with more serious thriller elements and some heartwarming scenes is splendidly done. They do not feel out of place. There are even a few nice twists that do not feel labored. By the end of Episode 13, I was wondering how the series could have another 3 episodes, but it did and it was done well too. The last episode feels like it has some filler moments so that it can become a full episode, but it's still not a significant problem.

The series also manages to highlight social issues like the struggles of the poor and caregiver stress. There is also a recurring theme of parental love and the lengths (sometimes touching, sometimes frightening) to which parents would go for the sake of their children.

The series is not perfect, of course. There are some slight plot holes and the depiction of dementia in the series seems a little unrealistic. But these flaws do not compromise the quality of the series.