There is a class full of delinquents that other schools do not accept. Within that class, there exists a ranking system called KO. Wang Da Dong is KO.3 as well as the class leader. He becomes best friends with another KO.3, Wang Ya Se, and KO.4, Ding Xiao Yu. When Lei Ke Si, a long absent student, returns to school, strange things begin to happen and Ya Se is suspected of being the culprit and legendary KO.2, who can hide his identity.