Seong Gi-hun is down on his luck, having accumulated enormous debts to loan sharks while becoming estranged from his daughter and ex-wife. In a subway station, a well-dressed man invites him to play a game of ddakji for money and offers an opportunity to participate in higher-stakes games. Gi-hun initially declines but reconsiders after his mother is diagnosed with Type 2 Diabetes and he has no way to pay for her medical treatment. He is sedated and awakens in a dormitory with 455 others, identified only by a number on their dark green tracksuits.