Kaiji Itou is a good-for-nothing loiterer who spends his days drinking beer and stealing hubcaps—that is, until he ends up being tricked by his former co-worker. Unable to suddenly repay his friend's huge debt all by himself, Kaiji is offered a shady deal to participate in an illegal underground gamble on a cruise ship. This turns out to be nothing more than the beginning of his new life of hell—thrown headlong into a life-threatening roller coaster of mind games, cheating, and deceit.