Korea has been taken over by aliens, and three agents from two different timelines spearhead the war against them. An unknown monster strikes them! One day, a single scream in an urgent phone call was heard.

A top-level national secret organization, aka BUG (Bureau of Unidentified Genes), ​​is dispatched to catch the unknown beast that appears in the city center. Veteran Jung Bong, principleist Hyo Chan, and passionate newcomer Ki Woong, the three Korea's top special agents are starting to counterattack!