Signal (South Korean TV series)

Signal is a South Korean television series written by Kim Eun-hee, directed by Kim Won-seok, and starring Lee Je-hoon, Kim Hye-soo, and Cho Jin-woong. Based on the 2000 film Frequency in premise and inspired by real-life criminal incidents in Korea, including the Hwaseong serial murders. The first season aired on tvN from January 22 to March 12, 2016, every Friday and Saturday at 20:30 (KST). In March 2024, a second season was confirmed in production.

The series received widespread acclaim from audiences and critics alike for its story and performances. It is also one of the highest-rated Korean dramas in cable television history with a peak audience viewership of 12.544%.

Plot
In present-day 2015, criminal profiler Park Hae-young (Lee Je-hoon) finds a mysterious discarded walkie talkie; inexplicably, the person at the other end, Detective Jae-han (Cho Jin-woong), is from the past, and addresses him familiarly, even though Hae-young has never met him. Hae-young is able to solve a 15-year-old kidnapping and murder case involving a former classmate from his childhood with Jae-han's help. The success of this case triggers the formation of a cold case team, led by Detective Cha Soo-hyun (Kim Hye-soo), who has been searching for Jae-han, her long-lost mentor and unrequited love, for the past 15 years.

With Jae-han's help from the 1990s, Hae-young solves other cold cases that have remained unsolved for years and is drawn into the mystery surrounding Jae-han's disappearance in the year 2000. As they try to fix the past and catch the criminals, unintended consequences follow in the present.

Main

 * Lee Je-hoon as Park Hae-young
 * The jaded and hotheaded criminal profiler who finds the walkie-talkie by chance, and uses his connection with Jae-han to solve cold cases.


 * Kim Hye-soo as Cha Soo-hyun
 * The first female police officer in the Special Task Force, she becomes the leader of the Seoul cold case squad. She has been searching for Jae-han, her mentor and unrequited love, for 15 years, believing him to be dead.


 * Cho Jin-woong as Lee Jae-han
 * The socially inept but virtuous and quick-tempered detective from the past who establishes a rapport with Park through the walkie-talkie. His timeline during his communication with Park spans from 1989 to 2000.

Supporting

 * Police officers
 * Jang Hyun-sung as Kim Bum-joo
 * The corrupt police superintendent.


 * Jung Hae-kyun as Ahn Chi-soo
 * The section chief and supervisor of the Seoul cold case squad who acts as Bum-joo's lackey but appears morally gray.


 * Kim Won-hae as Kim Gye-chul
 * A police officer who joins the Seoul cold case squad and often serves as comic relief.


 * Jung Han-bi as Oh Yoon-seo
 * A colonel.


 * Lee Yoo-jun as Jung Han-ki
 * A forensic scientist and member of the Seoul cold case squad, often seen with Detective Kim.


 * Kim Min-kyu as Hwang Eui-kyung
 * A junior officer that cleans up the Seoul cold case squad's work area and admires them.


 * Extended
 * Kim Hyun-bin as young Park Hae-young
 * Kang Chan-hee as Park Sun-woo
 * Hae-young's older brother who was convicted in the high school gang rape case and died by suicide after being released.


 * Yang Dae-hyuk as Hong Won-seo
 * A detective.


 * Lee Moon-soo as Lee Jae-han's father
 * Seo Ju-hee as Cha Soo-hyun's mother
 * Lim Hwa-young as Cha Soo-hyun's younger sister
 * Lee Do-yeop as Kim Jung-jae

Special appearances

 * Oh Yeon-ah as Yoon Soo-ah (ep. 1-2)
 * Lee Young-eun as Kim Yoon-jung (ep. 1-2)
 * Lee Si-a as Kim Won-kyung (ep. 2-4)
 * Kim Jung-young as Won-kyung's aunt (ep. 2-4)
 * Kim Ki-cheon as Lee Chun-goo (ep. 3-4)
 * Lee Dong-ha as Han Se-kyu (ep. 5-8)
 * Jung Suk-yong as Oh Kyung-tae (ep. 5-7)
 * Park Si-eun as Oh Eun-ji (ep. 5-6)
 * Choi Woo-ri as Shin Yeo-jin (ep. 5-6)
 * Yoo Ha-bok as Shin Dong-hoon (ep. 5-7)
 * Son Hyun-joo as Jang Young-chul (ep. 7, 11, 14, 16)
 * Lee Eun-woo as Shin Da-hye (ep. 7-8)
 * Lee Sang-yeob as Kim Jin-woo (ep. 9-11)
 * Lee Chae-kyung as Jin-woo's mother (ep. 10)
 * Seo Eun-ah as Yoo Seung-yeon (ep. 10-11)
 * Shin Yi-joon as Kang Hye-seung (young / ep. 11-14)
 * Kim Woo-suk as Lee Dong-jin (ep. 12-14)
 * Lee Jin-kwon as a bully (ep. 12)
 * Hwang Seung-eon as Han Do-yeon (ep. 13)
 * Jeon Su-ji as Kang Hye-seung (adult / ep. 13-14)
 * Seo Ji-hoon as Jang Tae-jin (ep. 14)

Reception
Upon its premiere, the series attracted attention for weaving actual cases into its plot and attained high ratings. With its finale rating of 12.54%, it is one of the highest rated Korean dramas in cable television history. It received praise for its solid acting, tightly-constructed plot and detailed and sophisticated direction; and enjoyed success internationally in China and Japan.

The drama went on to win several awards from different award-giving bodies, including Best Drama, Best Screenplay for Kim Eun-hee, and Best Actress for Kim Hye-soo at the 52nd Baeksang Arts Awards, as well as another Best Actress award for Kim and the Daesang (Grand Prize for Television) for Cho Jin-woong at the tvN10 Awards. Cho also won the Daesang at the 1st Asia Artist Awards for his performance.

Adaptations

 * A Japanese remake starring Kentaro Sakaguchi aired from April 10 to June 12, 2018, on Fuji TV.
 * On October 23, 2019, Unknown Number, a Chinese remake of Signal, started airing on Tencent Video.
 * On January 20, 2023, there was also a Thai remake of Signal called 23:23, which aired on True4U.
 * There is also an India remake of the series called Gyaarah Gyaarah (Web Series), which will stream in 2024 on Zee5.