一九九零年,六个小孩突然失踪了,同时,在国防部内,一群顶尖的科学家正研究着一项国家最高机密计划。 30年后的2002年,在同一韩半岛中,突然出现一宗连锁谋杀案,被杀者全部都是科学家。而南北韩的代表亦为这宗案件成立了专责的调查组,他们均配备了先进的装备以方 调查案件 。 纵使调查组布下天罗地网,可是罪犯仍然可以轻易逃脱。这一回,另外三名科学家遭绑架。而这些谋杀案却隐藏着一个玄机, 是他们都有一个共通的密码:“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...