It's the beginning of the Fourth of July weekend, but New York City Detective John McClane (Bruce Willis) isn't celebrating. He's had yet another argument with his college-age daughter Lucy (Mary Elizabeth Winstead), and received a crushingly routine assignment to bring in a young hacker, Matt Farrell (Justin Long), for questioning by the FBI. But for McClane, the ordinary has a habit of exploding into the extraordinary--abruptly hurtling him into the wrong place at the wrong time.
With Farrell's help, McClane slowly begins to understand the increasing chaos surrounding him. An attack is underway on the vulnerable United States infrastructure, shutting down the entire nation. The mysterious figure behind the scheme, Thomas Gabriel (Timothy Olyphant), stays several moves ahead of McClane as he implements his incredible plans, known to uber-geeks like Farrell as a "fire sale" (as in, everything must go!)