TV series
There are those who are born monsters, but there are also those who are made into monsters by people.
Detectives from the present and a detective from the past communicate via walkie-talkie to solve a long-time unsolved case.
Streaming, rental and purchase options
Checked Sep 2, 2026
Signal is available to stream on Netflix, Prime Video, The Roku Channel, and Tubi in United States. Use the direct links below to open the provider.
Detectives from the present and a detective from the past communicate via walkie-talkie to solve a long-time unsolved case.
Choose an episode, then use the watch options above for the show.
Episode 1
Profiler Park Hae-young hears a man calling his name through a discarded two-way radio. The voice starts talking about an unsolved crime.
Directed by Kim Won-sukGuest stars Jang Hyuk-jin, Oh Yeon-ah, Song You-hyun, Seo Jung-joon, Jeong Jong-yeol, Choi Hyun-joon, Lee Yeong-eun, Kim Soo-jin
Episode 2
The statute of limitations is lifted after the suspect's arrest. Hae-young joins Soo-hyun's team for the newly established cold case squad.
Directed by Kim Won-sukGuest stars Oh Yeon-ah, Song You-hyun, Seo Jung-joon, Sung Hyun-mi, Kim Ki-cheon, Lee Ki-seop, Lee Shi-a, Choi Hyun-joon
Episode 3
Reality changes after Hae-young exchanges information with Jae-han. Hae-young tries to work together with Jae-han in 1989 to prevent the next murder.
Directed by Kim Won-sukGuest stars Sung Hyun-mi, Kim Ki-cheon, Lee Ki-seop, Lee Shi-a, Lee Do-yeop, Hong Seok-bin, Nam Sang-ran, Kim Jung-young
Episode 4
The ninth victim is Won-kyung, the woman Jae-han loves. A driver turns himself in, but Soo-hyun and Jae-han determine that his son is the real killer.
Directed by Kim Won-sukGuest stars Sung Hyun-mi, Kim Ki-cheon, Lee Ki-seop, Lee Shi-a, Lee Do-yeop, Hong Seok-bin, Oh Jin-ha, Nam Sang-ran
Episode 5
Hae-young starts to investigate Jae-han's disappearance. Jae-han's former colleagues get suspicious about seeing Hae-young digging into the past.
Directed by Kim Won-sukGuest stars Choi Woo-ri, Kim Myeong-joong, Jeong Seok-yong, Park Si-eun, Yoo Ha-bok, Kang Joo-hee, Seo Ju-hee
Episode 6
Seeking vengeance for the events that lead to the death of his daughter, Kyung-tae commits a kidnapping after getting out of prison for burglary.
Directed by Kim Won-sukGuest stars Choi Woo-ri, Kim Myeong-joong, Jeong Seok-yong, Park Si-eun, Yoo Ha-bok, Sun Yul-woo, Im Cheol-soo, Lee Dong-ha
Episode 7
Jae-han arrests Se-kyu for the serial burglary case, but the culprit is freed after serving a short sentence; Kyung-tae still commits murder.
Directed by Kim Won-sukGuest stars Choi Woo-ri, Son Hyun-joo, Jeong Seok-yong, Park Si-eun, Yoo Ha-bok, Im Cheol-soo, Lee Dong-ha, Yoon Bok-sung
Episode 8
Soo-hyun and Hae-young notice a connection between the burglary case and Da-hye, the woman who killed herself twenty years ago.
Directed by Kim Won-sukGuest stars Lee Dong-ha, Lee Na-ra, Kim Ryeo-eun, Yoo Jae-ik, Yang Eun-yong, Hyun Sung
Episode 9
Hae-young learns that Chi-soo and Jae-han met in 1999 during a case in Inju. After serving time for the crime, Hae-young's brother had killed himself.
Directed by Kim Won-sukGuest stars Im Cheol-soo, Park Seong-hoon, Im Yong-soon, Lee Sang-yeob, Seo Eun-ah, Kim Yoon-hee, Yang Seung-geol
Episode 10
The bodies discovered in the mountains appear to be more victims of the 1997 serial murder case. Jae-han learns that Soo-hyun became team leader.
Directed by Kim Won-sukGuest stars Lee Sang-yeob, Seo Eun-ah, Lee Chae-kyung, Song Kyung-hwa
Episode 11
Hae-young and Soo-hyun arrest Jin-woo after coming to the conclusion that he is the killer. Hae-young asks Jae-han about the Inju rape case.
Directed by Kim Won-sukGuest stars Son Hyun-joo, Ji Hye-in, Lee Sang-yeob, Seo Eun-ah, Kim Yoon-hee, Park Eun-young, Kim Hak-sun, Hong Boo-hyang
Episode 12
Hae-young becomes a suspect for the murder of Chi-soo. Jae-han realizes who the principle offender of the attack on Hye-seung is.
Directed by Kim Won-sukGuest stars Kim Hak-sun, Hong Boo-hyang, Jeon Su-ji, Shin Yi-Joon, Seo Ji-hoon, Kim Woo-seok, Lee Jin-kwon, Sung Ki-yoon
Episode 13
Soo-hyun and the others mourn after confirming that the remains belong to Jae-han. Hae-young learns that Jae-han used to look after him in the past.
Directed by Kim Won-sukGuest stars Jeon Su-ji, Shin Yi-Joon, Seo Ji-hoon, Kim Woo-seok, Lee Jin-kwon, Hwang Seung-eon, Lee Jae-eun, Kang Chan-yang
Episode 14
Hae-young realizes the possibility that his brother could have been murdered after learning from Hye-seung that Sun-woo was not guilty.
Directed by Kim Won-sukGuest stars Son Hyun-joo, Jeon Su-ji, Shin Yi-Joon, Seo Ji-hoon, Kim Woo-seok, Shin Mun-sung, Sung Ki-yoon
Episode 15
Hae-young is arrested for the murder of Chi-soo. Soo-hyun hears Jae-han apologizing over the radio for not being able to prevent Sun-woo's death.
Directed by Kim Won-sukGuest stars Son Hyun-joo, Jeon Su-ji, Shin Yi-Joon, Seo Ji-hoon, Kim Woo-seok, Oh Ki-hwan
Episode 16
Hae-young is in critical condition after being shot while meeting with Sung-bum. In 2000, Jae-han has been captured by Bum-joo.
Directed by Kim Won-sukGuest stars Son Hyun-joo, Jeong Jong-yeol, Jeon Su-ji, Shin Yi-Joon, Seo Ji-hoon, Kim Woo-seok, Sung Ki-yoon
Episode information updated Sep 17, 2026
Lee Je-hoonPark Hae-young
Kim Hye-sooCha Soo-hyun
Cho Jin-woongLee Jae-han
Jang Hyun-sungKim Bum-joo
Jung Hae-kyunAhn Chi-soo
Kim Won-haeKim Gye-chul
Jung Han-biOh Yoon-seo
Lee Yoo-junJung Heon-gi
tvNSouth Korea
AStorySouth Korea
Studio DragonSouth Korea
BA EntertainmentSouth Korea
Baram PicturesSouth Korea
