Orphaned then taken in by his gambler uncle, Kim In-ha (Jin Goo) often hangs out with his friends in the basement of a movie theater. He unexpectedly befriends Choi Jung-won, a model student and the rich son of the theater owner. In-ha and Jung-won both fall for Min Su-yeon (Han Ji-min), the daughter of the projectionist at the theater.
When Su-yeon's father was killed by loan sharks, In-ha and Jung-won hatch a plan to avenge Su-yeon by setting fire to a gangster's hideout. But the fire spreads, accidentally killing the gang leader. In-ha is sentenced to seven years, while thanks to his family connections, Jung-won avoids jail time. As In-ha serves his sentence, Jung-won goes to the United States to study and Su-yeon decides to become a nun.
Seven years pass, and by pure chance, the three all end up working at the same casino. In-ha (Lee Byung-hun) and Su-yeon (Song Hye-kyo) fall in love, but are later separated when In-ha is forced to illegally immigrate to the U.S. He finds a job as a mafia hitman, and by a stroke of luck, again meets Su-yeon, and the two plan to get married. However, on their supposed wedding day, In-ha suffers a near-fatal gunshot wound and becomes comatose for 8 months. Unaware that In-ha is alive, the grieving Su-yeon returns to Korea.
In-ha eventually recovers, but Jung-won (Ji Sung) intervenes, saying that he is unworthy to love Su-yeon. In-ha decides to turn his life of misery around and becomes a professional gambler. He meets a business partner and, betting everything he has, returns to Korea to win back Su-yeon's love.