Areum is the younger sister of the doting Joonmyeon Kim. She lives as a normal high-schooler until a horrible incident throws her into the dark world of gangsters. She finds out that her loving brother is the leader of the gang Exo-K and even gets mixed up with its archrival, Exo-M. However, what the two gangs don't know that there is a bigger, more sinister gang who is their true nemesis.