Set somewhere around 2020 AD, Yesterday is the story of a reunified Korea, suddenly plagued by a spate of brutal murders of top scientists. Whoever is performing the killings is a highly-skilled paramilitary operative, familiar with government protocols and a wide array of military hardware. As the police dig deeper into the mystery, evidence of a secret government project and subsequent cover-up comes to light, and suddenly the cops are looking fora team of crack government-trained secret operatives instead of a serial killer.