Kanzaki Nao, a honest college student, receives 100 million yen (about $1,000,000) one day, along with a card saying that she has been chosen to participate in the "Liar Game". In order to win the game, she must trick other players into giving her their 100 million yen while her opponents are left in debt.
The objective of the first round is to steal the 100 million yen that is issued to her opponent, Kazuo Fujisawa, a former teacher of hers, who easily deceives her, while preventing her opponent from stealing her 100 million yen. Before the round ends, she comes across Shinichi Akiyama, a genius swindler, who helps her to succeed winning the first round. However, after the first round, a second round of Liar Game awaits them.
The second round of the Liar Game is taken place in a mansion. The 22 players who won the first round are given a jewel worth 100 million yen each as "Game Money" as they compete in a game. The 22 players vote either "Yes" or "No" when asked a random question. The minority of the result survives and the majority leaves with a debt, 100 million yen. The final person gets the 2.1 billion yen, 2.2 billion yen minus their 100 million yen, as the prize. Akiyama enters (as a substitute for someone who doesn't wish to continue in the game), wins the game, and then decides to split the prize money so that Nao and the people they had teamed up with to win the game could pay their debt. However, after paying off everyone else's debt, Akiyama doesn't have enough money to pay the cost of dropping out himself. He decides to continue playing the Liar Game to find out who is behind it, and then loses all contact with Nao.
A week later, Nao enters the Liar Game Revival Round, for those who lost previous rounds of the Liar Game. She intends to win the Revival Round in order to get the money necessary to pay the cost for Akiyama to drop out. The Revival Round is a "downsizing game" that has eight contestants besides Nao. One will be eliminated while the remaining eight will proceed to the third round. At the end of the Revival Round Nao is able to win and take everyone else's money with Akiyama's help. Nao figures that the Liar Game is actually a competition for people to be honest and upstanding: in each round, the LGT gives 100 million yen to each player and collects it at end of each round. But if the winner of each round gives back all the money to the other players and doesn't use their extra money to drop out, the LGT does not make a profit. This means that no one loses if everyone cooperates, but everyone loses if one person decides to become greedy for him or herself.
Soon the third round begins. Akiyama and the 8 winners of the Revival Round go in a bus with blacked-out windows to an abandoned airport, the location of the game. The game of the third round is the "contraband game", a team game in which each team must smuggle money out of an opposing country so it can be transferred to a third country. The two main countries in this game are labelled "Northern Country" and "Southern Country", and are represented by two adjacent rooms. Each team will take turns being smugglers and customs officials. When a team is the smuggling team, they must select one team member as the smuggler. The smuggler will get a briefcase, and take money from the fictional bank account and put it in the briefcase. Each player gets 400 million yen total: 100 mil already in the third country, and 300 mil in the opposing country. The briefcase can hold a maximum of 100 mil. The customs official team will select one member to be the customs official for that team. The smuggler and customs official will be put in a soundproof room with a one-way window for 10 minutes. During that time, the customs official can ask the smuggler questions, watch the customs official body langauge, etc, to figure out how much money is in the suitcase. They cannot touch the smuggler or briefcase. When the customs official is ready, they press a button (to disable the soundproofing) and say either "Pass", signifying they don't believe any money is in the briefcase, or "Doubt", signifying they believe the briefcase contains money. If the customs official says doubt, they must also say how much money they believe is in the briefcase. Thus there are four possible scenarios:
Scenario 1: Customs official passes. If this is the case, the smuggler has successfully smuggled any money in the briefcase.
Scenario 2: Customs official doubts, but there is no money in the briefcase. If this is the case, the smuggler will receive an indemnity from the customs official equal to half the amount of the money the customs official declared.
Scenario 3: Customs official doubts, and the amount of money in the suitcase is equal to or less than the declared doubt (unless the amount of money is 0). If this is the case, the smuggle is unsuccessful, and the customs official gets all the money in the briefcase.
Scenario 4: Customs official doubts, and the amount of money is greater than the declared doubt. If this is the case, the smuggler successfully smuggles the money and the smuggler receives an indemnity equal to half the declared doubt from the customs official.
The objective of the game is to smuggle all 300 mil in your bank account in the opposing nation out. The game will consist of 50 rounds; one round is having each team be the customs official team and the smuggling team once. After the 50 rounds, the team that has smuggled out the most money wins, and any money that remains in the bank accounts of the opposing country will be divided evenly between the members of the opposing team. There is an opportunity to win much money in this round. Not only because each player gets 400 mil as opposed to 100 mil, but because there are several ways to get money: from smuggling as the smuggler, from receiving indemnities as the smuggler, from catching smugglers as the customs official, and from the other team's unsmuggled money at the end of the game. It is revealed that the Akiyama and the 8 winners of the Revival Round are one team, the Southern Country, and 9 new characters form the Northern Country.