Fletcher Reede is a fast-talking attorney and habitual liar. When his son Max blows out the candles on his fifth birthday he has just one wish - that his dad will stop lying for 24 hours. When Max's wish comes true, Fletcher discovers that his mouth has suddenly become his biggest liability.
On July 2, a giant alien mothership enters orbit around Earth and deploys several dozen saucer-shaped 'destroyer' spacecraft that quickly lay waste to major cities around the planet. On July 3, the United States conducts a coordinated counterattack that fails. On July 4, a plan is devised to gain access to the interior of the alien mothership in space, in order to plant a nuclear missile.
Advertising executive Nick Beame learns that his wife is sleeping with his employer. In a state of despair, he encounters a bumbling thief whose attempted carjacking goes awry when Nick takes him on an involuntary joyride. Soon the betrayed businessman and the incompetent crook strike up a partnership and develop a robbery-revenge scheme. But it turns out that some other criminals in the area don't appreciate the competition.