Yesterday

1990. A number of children suddenly disappear. Meanwhile, the Ministry of Defense selects an elite group of scientists for a top-secret mission. Then, 30 years later ... The year is 2020 on a reunified Korean Peninsula. A string of murders is committed against retired scientists. The Special Investigations (SI) unit staffed by a crack team from the former North and South Koreas and outfitted with the latest technology is brought in to investigate. The killer, however, far from being deterred, taunts them with a signature pendant at every murder scene. In an act of devilish boldness he even kidnaps the son of the investigation team's leader, Seok. Then, in a stakeout, Seok manages to shoot dead one of the murderer's underlings. Cloaked in the man's clothes, however, is Seok's son, now dead by the hand of his father ... Meanwhile, in the megapolis Intercity, the chief of police is kidnapped right in front of his heavy security detail and the culprit leaves another pendant at the scene. The chief's daughter, Heesu, a talented criminal psychologist quickly joins the investigation to find her father. Soon, Seok discovers that he and Heesu share an uncanny bond...