Lights, camera, action!
It's just a normal 4th of July weekend in the U.S. of A…as far as the good people of earth know. You know: bbqs, pool parties, and trips to the nearest fireworks stand.
Oh yeah: and mass alien invasion. In the film's opening scene, we (the lucky audience) see a spaceship heading straight for earth. This is not what the Star Spangled Banner meant by "O'er the land of the free and the home of the brave."
Sure enough, the alien ships show up over major cities all over the world, and humans have zero idea of what to do. At first, there's some hope that the aliens are there to make friends, and so nobody really gets an attack plan together.
Big mistake.
Genius cable company employee David Levinson realizes that the aliens are up to something more devious than grilling wieners, but he doesn't get to tell the President until it's too late. So, the spaceships end up obliterating tons of major cities across the world, including several in the U.S.
Then, when the U.S. tries to retaliate, they realize that they can't penetrate the aliens' force shields. Lots of military lives are lost figuring that out.
So, what to do? Well, David (who just happens to be the estranged husband of the President's communications director—hmm, that's pretty lucky), uses his super-smarts and access to the White House to hatch a plan for a world offensive that hinges on his ability to get up into the alien mother ship and use his Macintosh laptop to put a virus in their entire defense system.
He can't do it alone, though. For one, he can't fly a plane—but what do you know, they have ace fighter pilot Steve Hiller on hand to take on that job when it comes up.
There are lots of others who help out, too: We have Julius, David's dad, who hangs around the problem-solvers and offers feedback (or criticism—thanks, Dad). He even ends up giving David the whole idea for the virus by harassing him about his health.
We should also mention Secretary of Defense Nimziki, who gives the President bad advice at basically every turn. He doesn't seem to have bad intentions…just terrible instincts. Which is why the President eventually fires him.
Then, there's Russell, who is pretty much a minor character for most of the film but gets a big moment there at the end. There's zero chance he'd be allowed anywhere near a special military mission under normal circumstances, since he drinks on the job and has seemed a little unhinged and paranoid in the past…but these aren't normal circumstances.
So, when Our Heroes need someone with flying experience to help out with a mission, and he just happens to be at Area 51 while they're making the plans, he gets the nod to go up and fight the aliens.
And it's a good thing, since when everyone else runs out of ammo, he's the only one who can come to the rescue. He proves himself super-brave here. In fact, when his missile launch jams, he actually drives his plane up into the alien spaceship to make sure his explosives connect with the visitor craft's major weapon.
That does the trick, and the entire ship explodes. Not only does Russell's bravery help the Prez and his crew at Area 51 out, but it also shows them that the best way to destroy the alien ships is to fire missiles at the spaceships' major weapon.
David and Steve might be the big heroes of the film, but Russell definitely plays a big role in figuring out how to take down the aliens once and for all.
Finally, alongside all of the above, there are a bunch of romance plots going on for both David (with wife Connie) and Steve (with girlfriend Jasmine) along the way. But it's not all sunshine and lollipops: the President loses his wife to injuries she sustained in the alien attacks.
David and Steve's mission is successful, and a coalition of forces from across the world (cleverly organized using Morse code to avoid alien detection) leaps into action to destroy the ships. The world—and the Americans' holiday weekend—is saved.