Seong Gi-hun is down on his luck, having accumulated enormous debts with loan sharks while becoming estranged from his daughter and ex-wife. At a subway, a well-dressed man asks him to play a game of ddakji for money, and offers an opportunity to play more games with much higher stakes. Gi-hun accepts, is knocked unconscious, and awakens in a dormitory with 455 others, identified only by numbers on their tracksuits. A group of masked staff in pink jumpsuits arrive and explain that the players are all in dire financial straits, but will be given billions of won in prize money if they can win six games over six days. The games are overseen by the Front Man, who is masked and dressed in black. Gi-hun befriends Player 001, an elderly man suffering from a brain tumor. He also recognizes two other players: Cho Sang-woo, a childhood classmate who became an investment broker, and Player 067, a pickpocket who stole Gi-hun's money after he won a horse race wager. The first game is a deadly iteration of Red Light, Green Light, where anyone caught moving is shot dead on the spot. With help from Sang-woo and Player 199, Gi-hun finishes the game alive.