Down-and-out Seong Gi-hun runs into oppa Gong Yoo at the subway station. He is tricked into playing a ddakji game with the other man, agreeing that the winner can either take 100,000 won or slap the loser! Gi-hun fails repeatedly, and just when he is about to be slapped silly, he finally turns the tide, takes the prize money, and receives a mysterious card at the same time. The man tells him that if he wants to win more money, he can call the number on the card to continue participating in the game.
Seong Gi-hun is a real loser. He has no money, no job, and is addicted to gambling, living off his mother's pension. His wife divorced him and took their daughter to remarry, and now the whole family is going to immigrate to the United States with her stepfather. He wants to get his daughter's custody back, but the condition is that he must have a certain financial ability. However, he has no other way, so he has to reluctantly call the number on the mysterious card.
Late at night by the roadside, a van comes. The driver is tightly wrapped up in red clothes. After Gi-hun gets in the car, he is immediately knocked out by a mist. When he opens his eyes, he finds himself in a place like a concentration camp. Everyone is wearing the same clothes with numbers marked on their chests. He is number 456, which is the same as the number on the big screen. Later, he learns that there are 456 people here in total. At this time, the door of the room opens, and a group of game executors in red clothes and masks appear, announce the game rules, and let all participants sign a contract, telling everyone that as long as they pass six games, they can get a huge bonus. The participants all stare at the glittering ball on the ceiling.
The first game starts, and hundreds of people are taken to an outdoor venue. In this unfamiliar environment, Gi-hun unexpectedly meets his childhood friend Sang-woo. He is the only one from Ssangmun-dong who was admitted to university, even Seoul National University. Now he is also reduced to the same situation as himself because of debts. At this time, a group of people look at the huge turning doll in front and realize that they are going to play the 123 Wooden Man game. The game starts. As the first person who can't stand still is shot dead, a group of people who have never seen the world are scared out of their wits and run back desperately, but they are shot dead one after another for breaking the rules. A lot of people are eliminated in this round. The music starts, but the remaining people dare not move. At this time, the old man No. 001 calmly continues the game. Inspired by him, everyone truly understands the rules of the game. Our male protagonist obviously reacts half a beat slower, which forms a sharp contrast with his clever childhood friend and the tough North Korean female protagonist Jung Ho-yeon. While he is in a daze, Sang-woo and the female protagonist have already crossed the finish line. Gi-hun hurries to make an effort, but steps on a corpse's arm. At this time, the huge doll just turns its head, and Gi-hun is about to fall. A Pakistani guy stretches out a strong hand, pulls his collar, and saves his life. There are only 3 seconds left. Gi-hun takes a big stride and leaps over the red line. As the time returns to zero, all the people left on the field are shot dead, and the game ends.
At this time, the manipulator behind the scenes is sitting in front of the big screen, enjoying this cruel game. The mysterious game venue turns out to be an isolated island in the sea.