A group of teenagers discover a secret about their favorite teacher and his partner. Once he was someone just like them but times change, and things can also change a person. There children dig into the past and uncover things that shouldn't be brought up and uncover old wounds. 

Kangin is just your average teacher. Eunhyuk, Donghae, Sungmin, Kyuhyun,  and Heechul are just ordinary high school kids. One early morning these bored teenagers stumble upon their favorite teacher running late which results in a sort of...story telling, before class starts. 

Yes i know, I at summaries. Just read it to understand ^^