Dressed as a schoolgirl, Detective Chun Jane, surrounded by Korean prostitutes, goes undercover to stop Hammer, a member of the Korean mafia who traffics women to the yakuza. When the yakuza arrives, Jane attacks the mafia members and almost beats up every one of them on her own. However, after Hammer is caught, the yakuza turns out to be another detective who blames Jane for destroying his plan to catch the real yakuza member. Being the spunky, hot-tempered fireplug that she is, Jane does not take these words lightly and becomes quite antagonistic towards Detective Cho.
Later, the heads of the police department are trying to find the location of Cha Young-jae, Bae Doo-sang's, the leader of the suspected human trafficking scandal, right hand man. Cha had been willing to testify against him, but after an attack Cha quickly fled the scene. In order to find Cha, the head of police decides that Cha's daughter Seung-hee needs to be followed because surely her father will try to contact her. Soon afterwards, after seeing Jane still dressed in her school uniform, the head decides that Jane will attend the school as a student and keep a close eye on Seung-hee. Jane of course dislikes the idea, she is thirty and hated high school, and demands that she should be a teacher instead of a student, but her uncle, who is also her ranking officer, basically says that she is such an idiot that there is no way that she could teach a class. So, against her will, an angry, spunky woman is sent back to school.
Always a bit hostile, Jane soon unleashes her fury upon a girl gang and later a group of boys hired by said girl gang. She is constantly in trouble with her P.E. teacher who seems to view her as some type of social deviant, and she has a number of misunderstandings with other girls. However, she is eventually able to find a comfortable position at the school, but when she finally accomplishes this Detective Cho goes undercover at the same school.
She's on Duty is a decent film. It takes an old and tired theme and adds new life to it. This is mainly accomplished through the acting of Kim Seon-a who is probably best known for her work on the drama series My Name is Kim-sun. Kim is a spunky and very cute woman who looks twenty instead of thirty and her high energy and exaggerated movements make for an enjoyable film watching experience. However, outside of Kim's performance this film leaves a lot to be desired. There are revelations that can be seen a mile away and some scenes are quite mawkish, but overall She's on Duty is not too bad and it is at least good enough to tickle your funny bone once or twice.