Kim Sun-a Chun Jae-in, undercover cop Gong Yoo Kang No-young, boy at school, Jae-in's neighbour Nam Sang-mi Seung-Hee, daughter of mob boss Kim Sang-ho Detective Kang Noh Joo-hyun Detective Chun, Jae-in's uncle and boss Hong Soo-a Jo Hye-ryung Oh Gwang-rok Bae Doo-Sang, mob boss of the Whacker gang Park Sang-myeon Class teacher Kim Gab-soo Cha Young-Jae, second mob boss, Seung-Hee's father Ha Jung-woo Detective Cho Choi Bool-am cameo Lee Beom-soo Math Teacher (cameo)