Elliot Brindle, a meek salesman, loses his job despite his debt and the people who depend on him: Michael, his mentally handicapped brother; Shelby, his pregnant fiancee; and an unnamed, abusive father. Elliot receives a mysterious phone call that offers him $1,000 to assertively kill a fly that has been harassing him. After Elliot checks his bank account online and sees that he has been credited, he accepts the next challenge: to eat the dead fly. The caller explains that he will be offered a series of thirteen challenges, each of which will result in greater rewards. If he fails to complete any of them, interfere in the game, or reveals the game, he will forfeit all the money.