When her son who lives in a single room is given an outrageous $1,000 water bill, a mother decides to become a detective and find out what is behind it.
| Actor | Role |
|---|---|
 Park Ji-youngLee Mi-kyung | Lee Mi-kyung |
 Jo Bok-raeGae-tae | Gae-tae |
| KKim Dae-hyunLee Ik-soo (#404) | Lee Ik-soo (#404) |
 Heo Jeong-doKang Ha-joon (#403) | Kang Ha-joon (#403) |
 Baek Soo-jangOh Deok-goo (#301) | Oh Deok-goo (#301) |
 EsomKyung Jin-sook (#402) | Kyung Jin-sook (#402) |
 Lee Sung-wookLee Tae-gil | Lee Tae-gil |
 Oh Chang-kyungPark Se-joo | Park Se-joo |
 Kang Jin-ahConstable Song | Constable Song |
| KKwak Jin-mu#303 | #303 |
 Jeon Go-woonExamination Graduate Student | Examination Graduate Student |
 Kwon O-kwangExamination Graduate Student | Examination Graduate Student |
| WWoo Moon-giGame Boy | Game Boy |
| WWoo Sang-giDelivery Man | Delivery Man |
 Ahn Jae-hongSinchon Seolleongtang Civil Service Examination Student | Sinchon Seolleongtang Civil Service Examination Student |
 Hwang Seung-eon(uncredited) | (uncredited) |
 Kang Bong-sung(uncredited) | (uncredited) |