어느날 갑자기 서울은 The terrible variation virus that suddenly hit Seoul one day! Yeon-woo who has been on a school trip to Seoul, is so singing about the idea that he can get acquainted with the same class so-yeon, who was usually unrequited love. Unidentified cells appeared in front of The Yeon-woo's Class while sightseeing in Seoul. The math trips of classmates like the actors turn into hell because of the cells that turn the infected into a ferocious figure when they come into contact...! Can Yeon-woo escape Seoul safely?