KO One is a class designed especially for the delinquents and rejects that other high schools would not accept. Even so, everyone in the class is loyal to the leader, Da Dong, KO.3, and would die for friends. Tied for #3, Ya Se, and #4, Xiao Yu soon join the class and out of some fortuitous events, their lives become tied together and they become best buddies. Another student, Lex, who had been gone for a whole semester, rejoins the class. Although Lex seems like a weak kid with only good intentions, Ya Se suspects Lex is KO.2 because legend say #1 and #2 are capable of concealing their true identities. At the same time, incidents start to occur and the culprit always leads to Ya Se. Is Ya Se wrongly accused? Will the class be able to stand the politics or will it be driven apart?