Sukgyu has always been in the shadow of his classmate Jinwoo, whether it is in sports, academics, or popularity with the girls. He has a crush on Sohee, and so does Jinwoo. After another day of falling short, it seems that Jinwoo actually reciprocate his feelings, giving him an uplift to try and do better.

One day, after going to sleep early for a school trip the following day, Sukgyu wakes up late and his parents off handedly mention him that the trip was one month ago, and that he already came and went. What is the reason between this gap in memory? Not a single one of them realized that their days of normalcy were about to end, as a threat named the "Infected" was about to rise...