Gap-dong (Korean: 갑동이; RR: Gapdongi) is a 2014 South Korean television series starring Yoon Sang-hyun, Kim Min-jung, Sung Dong-il, Kim Ji-won and Lee Joon. It aired on cable channel tvN from April 11 to June 14, 2014 on Fridays and Saturdays at 20:40 (KST) for 20 episodes.^[1]

The series is based on the real-life Hwaseong serial murders.

In 1986, the (fictional) city of Iltan in Gyeonggi Province: A young girl gets brutally murdered by an unknown person on a dark night. As the city is gripped by a succession of serial killings, a total of nine murders within a twelve-kilometer radius since 1993, the police conclude that a man they've nicknamed "Gap-dong" is behind the crimes. Detective Yang Cheol-gon is convinced that the actual killer is Ha Il-sik, a resident of the town who is intellectually challenged. His attempt to arrest the suspect fails as Ha commits suicide to prove his innocence. His death inspires his son Moo-yeom to become a police officer to clear his father's name and restore his honor.

Seventeen years later, Moo-yeom is a police detective who spends his career chasing dead ends and helping juvenile delinquents. After the statute of limitations on the case expires, Moo-yeom becomes resigned to the belief that Gap-dong is dead. But then a series of incidents occur in the town that bear an eerie resemblance to Gap-dong's crimes. Cheol-gon, now a well-decorated officer, has recently transferred back to Iltan, and to his dismay, Moo-yeom joins his investigation team to catch Gap-dong once and for all.

In this table, the blue numbers represent the lowest ratings and the red numbers represent the highest ratings.

• This drama airs on a cable channel/pay TV which normally has a relatively smaller audience compared to free-to-air TV/public broadcasters (KBS, SBS, MBC and EBS).

• It aired in Thailand on Workpoint TV beginning March 9, 2015.^[7]
• In Hong Kong, Macau, Sri Lanka and Southeast Asia, the drama began airing on tvN Asia with a variety of subtitles on 2016.