Pemeran Hello Monster

Seo In Guk (서인국)

as Lee Hyeon

Pemeran Utama

Jang Na Ra (장나라)

as Cha Ji An

Pemeran Utama

Park Bo Gum (박보검)

as Jung Seon Ho

Pemeran Utama

Choi Won Young (최원영)

as Lee Jun Ho

Pemeran Utama

Lee Chun Hee

as Kang Eun Hyeok

Pemeran Pembantu

Min Sung Wook

as Son Myeong U

Pemeran Pembantu

Kim Jae Yeong

as Min Seung Ju

Pemeran Pembantu

Son Seung Won

as Choi Eun Bok

Pemeran Pembantu

Hong Hyun Taek

as Lee Hyeon [Young]

Pemeran Pembantu

Hong Eun Taek

as Lee Min [Young]

Pemeran Pembantu

Doh Kyung Soo (도경수)

as Lee Jun Yeong

Pemeran Pembantu

Park Ji So

as Cha Ji An [Young]

Pemeran Pembantu

Park Jae Woong

as Do Jae Sik

Pemeran Pembantu

Im Ji Eun

as Hyun Ji Su [Police officer]

Pemeran Pembantu

Nam Kyung Eup

as Kang Seok Ju [Police chief]

Pemeran Pembantu

Shin Jae Ha (신재하)

as Park Dae Yung [Murderer] (Ep. 4-5, 8, 13)

Bintang Tamu

Kim Jong Gu

as Sin Jang Ho (Ep. 5)

Bintang Tamu

Yoo Jae Ik

as Choi Jeong U (Ep. 5)

Bintang Tamu

Seo Young Joo

as Lee Jeong Ha (Ep. 6-7)

Bintang Tamu

Yeo Woon

as Lee Jin U (Ep. 7)

Bintang Tamu

Ko Kyu Pil

as Park Su Yong (Ep. 9)

Bintang Tamu

Lee El

as Kang Seong Eun (Ep. 9-10)

Bintang Tamu

Kang Eui Shik

as Seung Min Yeok (Ep. 15)

Bintang Tamu

Kim Ji An

as [Missing child] (Ep. 15)

Bintang Tamu

Byun Joon Suk

as Ji Won [New team member] (Ep. 16)

Bintang Tamu

Lee So Yun

as Ha Yun Ji

Bintang Tamu

Im Sung Eon

as Ji Hyeon Suk

Bintang Tamu

Hwang Min Ho

as Do Jae Hun

Bintang Tamu

Shin Dong Mi

as Yang Eun Jeong

Bintang Tamu

Tae In Ho

as Yang Seung Hun

Bintang Tamu

Ryu Seong Hyeon

as Lee Han Cheol [Prisoner]

Bintang Tamu

Park Geon Rak

as [Prison officer]

Bintang Tamu

Kim Ki Wook

as [Pillow store employee]

Bintang Tamu

Bae Gi Beom

Bintang Tamu

Dong Yoon Seok

Bintang Tamu

Lee Seung Hun

Bintang Tamu

Kim Jin Won

Sutradara

No Sang Hun

Sutradara

Kwon Gi Yeong

Screenwriter