ArchiveGuy did pretty well … here’s a bit more.
The Senate is divided between the Loyalists (who like things the way they are–Padme, Bail Organa, and some other people) and the Separatists (the Trade Federation and their ilk). Someone is trying to kill Padme. Obi-Wan and Anakin are appointed her bodyguards. Eventually, Anakin takes Padme to go hide out on Naboo, and Obi-Wan goes in search of the bounty hunter who was carrying out the job. He ends up on the planet Camino (which has been erased from all the records in the Jedi library), and finds that the Caminans (?) have been working away for ten years, filling an order for a clone army placed by a Jedi Master who may have been dead before the order was even placed. I’m kinda fuzzy on that. Anyhoo, the clones are being grown from aforementioned bounty hunter, Jango Fett, whose only request aside from his pay was that he get an unaltered clone to keep as his son, named, naturally, Boba.
Back on Coruscant, Palpatine is voted “emergency powers”, and uses them to create an Army of the Republic, which Obi-Wan just conveniently found.
Over on Naboo, Anakin is trying to get into Padme’s pants, she’s ineffectively shooting him down, and he’s somewhat bothered by dreams he keeps having about his mother. He and Padme go to Tatooine, find that Shmi was sold, then freed, and married to the guy who bought her. Upon finding his farm (which, naturally, looks quite familiar), Anakin is told by his stepfather (and stepbrother Owen) that Shmi was kidnapped by the Sand People, and has been gone over a month. Anakin goes to find her, and she dies on him before he can get her out. He then proceeds to slaughter every Tusken Raider in sight, men, women, and children. (Unfortunately, we didn’t actually get to see that.)
Meanwhile, Obi Wan has followed Jango Fett to Geonosis, where he finds droid factories making battle droids, and discovers that the Separatists are being led by a guy named Dooku/Darth Tyrannus. He gets caught, they do the “Join me and we’ll rule the galaxy”/“I’ll never join you” stuff. Anakin and Padme arrive to rescue Obi-Wan, get caught themselves, and everybody’s sentenced to death.
During the Roman Coliseumesque execution, Jedi Master Shaft comes in and tells Count Dooku that “This party’s over.” (That line cracks me up every damn time.) Then a mess o’ Jedi in disguise take on a boatload of battle droids. Windu kills Jango, Boba holds the bucket helmet and mourns. The Jedi are pretty much surrounded and beaten … till Yoda shows up with all the clones in the frickin’ galaxy. The clones, incidentally, wear armor that’s about three millimeters off from a stormtrooper outfit.
Clones kick Droid ass. Anakin and Obi-Wan go after Dooku, the fight, Obi-Wan gets singed in a couple places, Anakin loses his right arm. Then Yoda shows up. This is where we discover exactly why he’s later referred to as a “great warrior.” Tiny green can of whoop-ass. See the movie if only for this scene.
Dooku gets away, Anakin and Padme get married in secret, and as you see Chancellor Palpatine and the Loyalists survey about half a million clone troops preparing for battle … you slowly realize that the same guy is in charge of both sides of this war.
The end.