True friends watch out for one another and protect each other in difficult situations. Four childhood friends - Lee Joon Suk (Kim Min Joon), Han Dong Soo (Hyun Bin), Jung Sang Taek (Suh Do Young) and Lee Shi Un (Kim Joong Ho) - were inseparable while growing up and helped each other out of the petty scrapes and skirmishes as teenage delinquents in Pusan. But their delinquencies take a much more dangerous form in adulthood.