Aliens arrive in a gigantic mothership and prepare to invade earth. Huge daughterships get sent to hover above major cities all over earth. They use earth's satellites to communicate and time their attack which messes up TV signals. No one knows if they're good or evil except Jeff Goldblum who figures out they're playing chess and are about to checkmate earth.
On July 2nd the aliens launch their attack with their evil green rays which wipe out entire cities. They kick earth's collective ass and kill millions of people - but sadly not the lame US President, his cronies and Jeff and his eccentric father, all of whom escape on Airforce One just in the nick of time as Washington DC is getting vaporised. America's puny military response is no match at all for the aliens' vastly superior weaponry and the US fighter planes all get shot down including that of big mouth Will Smith who (regrettably) survives and even captures a snakelike alien pilot!
July 3rd: Airforce One lands at Area 51 which everyone except the president knew about. The large number of scientists there has been studying the aliens and their technology at great expense for 40 years since the Roswell incident but hasn't yet learnt a goddamn thing.
Later the captured alien takes control of the president's mind for a few seconds and nearly kills him but it is shot dead. Now the president knows that the aliens are evil so he finally authorises the use of a nuclear weapon - which has no effect.
The aliens are doing nothing instead of finishing the job. So Jeff Goldblum gets drunk, rolls around on the floor and then has an earth-shatteringly great idea! The enormously more advanced enemy can be brought to its knees by a computer virus running on a humble 1996 laptop.
July 4th: Will Smith marries his prostitute girlfriend. Then Jeff and Will take the Roswell alien aircraft armed with a nuclear weapon and fly directly to the mothership which takes control for them and handles docking. An alien sees them but does nothing despite being able to take control of their minds and kill them. So they duck down and hide for a while. Meanwhile on earth the daughterships are moving towards their new target cities, including Area 51. Earth's top gun fighter pilots are all dead but the airforce have had one day to train up new, inexperienced fighter pilots to fly the remaining fighter jets.
Finally Will and Jeff decide to act. Jeff somehow sends the computer virus to the alien computers which fortunately are not just compatible with ours but are also every bit as insecure and buggy. They also fire off the nuke. This action somehow un-docks them and enables them to escape just in the nick of time as the nuke explodes destroying the entire mothership. However, lots of daughterships are still in orbit and are gradually getting closer to their new targets.
The amateur pilots take off after a rousing speech from the President. They kick alien ass where the top gun airforce aces couldn't only a couple of days before. The evil green ray starts firing up but one pilot becomes a suicide bomber and flies into it causing a chain reaction of explosions in the daughtership eventually culminating in crash down in the New Mexico desert. The good guys (USA) now know how to defeat the daughterships so they inform the rest of the planet by Morse code and presumably all the daughtership meet the same fate.
The cast meets in the desert. They laugh, smoke cigars and watch the burning daughtership wreckage. Earth is saved on July 4th.