Seong Gi-Hun (Lee Jung-jae) is a kind-hearted, compulsive gambler who is in enormous debt. His elderly mother provides him with small amounts of cash, which he then gambles away, in hopes of earning more. He attempts to be a responsible father to his little daughter who lives with her mother, and her financially stable stepfather. Despite having no money, he finds a way to get a gift for his daughter’s birthday. However, he is a struggling working-class man who at one point signed a contract to sell one of his kidneys. Until one day, when he gets a chance to earn a great deal of money.