Dong-goo,alowlifethug,hasalwaysbeenlivingahopelessmiserablelife.Oneday,heaccidentallyobtainsabankbookwithsuchalargeamountofmoneyasmuchasonebillionwon.HetravelsdowntoBusaninordertotrytoobtainthePINnumberforthebankaccount.AsDong-goomeetstheeightyearoldboy,Bok-gi(JoWon-bin),whobelievesDong-gooishisdad,andtheboy’smother,Ae-sook(HongAh-reum)inBusan,theirstorybegins.