Didn't play Halo 1 or Halo 2? Don't have any clue what the story is before Halo 3 starts off? It's the Halo Puppet Show to the rescue!
HaloCovenant: Hi, we're a bunch of allied aliens and we're here to destroy all of you because our gods told us to. No hard feelings.
Humans: Crap. We're outnumbered and out-technologied. Good thing we've just completed training on 30 or so Spartan-II troopers.
Spartan-IIs: We were abducted when we were children, bionetically boosted and put into powered armor suits as expensive as spaceships. So we're gonna turn the tables. No hard feelings.
Covenant: We can burn planets. Including the one you're on.
Master Chief: Well, I'm the last one left. On the last ship left of the last planet left before they get to Earth.
Cortana: And I'm in your suit. Let's escape randomly and land on that thing they revere.
Covenant: Don't mind us, we'll get our act together and then get down there and squish you.
Cortana: Okay, we're on this Halo thing. The captain was captured, go save him.
Master Chief: Done.
Captain Keyes: Thanks. They say this Halo thing's a weapon, go find the control room.
Master Chief: Sure thing.
Master Chief: Nice control room.
Cortana: Lemme get into that planet computer.
Giant Cortana: Hot damn! I know everything, like the fact that something horrible is on this planet. The captain's gonna do something stupid, stop him!
Master Chief: But what abou--
Cortana: NOW! @_@
Master Chief: I found this hidden elevator going way down into someplace even the Covenant are afraid to go. Let's go inside.
Dead Trooper: I'm afraid I can't be much conversation. Here, watch the last thing I recorded before dying.
Recorded Captain Keyes: Strange, all these Covenant died of wounds from their own weapons. Well, let's go deeper in here and split up.
Recorded Little Balls of Hate: *brlblblbl*
Recorded Marines: OMGWTF x_x
Master Chief: Crap. Better get out of here.
Formerly Open Door: I like being locked better.
Master Chief: I'll turn around dramatically, then.
Flood: We're tiny organisms that zombify anything that moves. Also, there's a metric ton of us. Oh, and blrrblblbl!
Master Chief: Okay, killed all of them. Boy that's a lot of zombies and walking tentacled basketballs. Let's escape.
Monitor: Hello! I am a floating cybernetic eyeball. I am glad to see you are here to do your assigned duty. Follow me.
Master Chief: Dude, you can teleport? Hax!
Monitor: Welcome to the Library. See that key over there in the huge chasm? You need that to activate Halo. But to get it, you need to bring down that huge elevator. To get to it, you need to go through the same hallway thirty goddamned times and kill more enemies than you've killed so far in the entire game.
Master Chief: This is going to suck.
Master Chief: That sucked. Well, got the key now.
Monitor: Let's go to the control room! I'll take the key.
Master Chief: ........but... you can FLY... why didn't you--
Monitor: No time to waste! Teleport AWAY!
Master Chief: This was a faster way back.
Monitor: Ah, good old control room. Have the key back. Now activate Halo!
Master Chief: Okiedoo.
Monitor: Hm. Nothing happened.
Giant Cortana: Neener neener! I stopped it from inside.
Giant Cortana: I've been in here for like ten hours watching you help that asshole get set to slit our throat!
Master Chief: Nah, he's a friend.
Giant Cortana: Oh, he's your buddy? Your pal, your chum? Halo isn't a weapon against the Covenant - it KILLS EVERYTHING IN THE GALAXY!
Master Chief: ...really?
Monitor: Yup. This installation's pulse isn't so good, but once the other installations kick in, everything in the galaxy dies. Well, everything big enough for the Flood to use as a zombie host. The Forerunners who built Halo couldn't kill the Flood, so they figured they could at least starve them to death. Kind of stupid of them to keep a few as samples, though.
Master Chief: Well I can't do that.
Giant Cortana: Me, inside your head. Now.
Master Chief: Yoink!
Monitor: Okay, then I'll find someone who can. Deus Ex Machina With Lasers, kill him.
Deus Ex Machina With Lasers: Gladly! Bzap!
Master Chief: Why'd I start with a plasma pistol and a shotgun if I had the rifle in the cutscene? That doesn't make any sen--
Cortana: Okay, he's gonna kickstart Halo without the key. Let's bust up the three generators that control Halo's weapon, that way he'll be caulk-blocked.
Master Chief: Can I do it without going back through half the game but backwards?
Master Chief: Sigh.
Master Chief: Done.
Cortana: Okay, let's teleport to captain Keyes. If we wanna destroy Halo, we can do it by blowing up the crashed Pillar of Autumn.
Master Chief: Teleport?
Cortana: I can fake it once for plot reasons. Zoom!
Master Chief: Wait, I'm back on the goddamned alien ship?
Cortana: The flashback tour continues! Save the captain again!
Master Chief: He's a big pile of Flood and tentacles now. Eew.
Cortana: You know what he'd want us to do.
Master Chief: Got his neural chip! Now we can get access to the ship and blow it up.
Cortana: ...I don't think he'd have wanted us to punch his head in and rip out part of his brain.
Master Chief: Whatever. I'll hitch a ride.
Master Chief: That was a long flight. Okay, let's end our flashback tour by going through the first area of the game, this time with zombies.
Cortana: You're the boss. Okay, self-destruct started.
Monitor: im in ur ship, downloadin ur earth recordz
Cortana: Son of a bitch! Let's blow up the reactor, that'll do it.
Master Chief: Blow up part that glows, got it.
Master Chief: Okay, grenades tossed up exhaust pipes. Reactor gonna blow up.
Cortana: Let's escape. We have three kilometers of ship to go through in five minutes to our pickup point.
Master Chief: Hey, free Warthog!
Master Chief: That was awesome. Good thing I can pilot the last starfighter this ship has in the hangar.
Cortana: And we're clear! The ship will blow up and crack Halo in two, causing it to collapse in on itself and crush whatever's left on the surface. Mission accomplished!
Master Chief: Anybody left alive except us?
Cortana: Nope. Let's go back to Earth.
Halo 2Sergeant "The Black Guy" Johnson: I've inexplicably survived. Have some new and improved armor!
Master Chief: Nice space station orbiting Earth. We're here for some press conference, right?
Johnson: Yes, nothing more. Nothing could crash this party. What could go wrong? I have a bad feeling about this. Good thing I retire in three days. How I love my wife. And our new boat, the Live4Ever.
Admiral: Medals for everybody! Miranda Keyes, you're a hot girl whose father died in the first game. Have a medal for his coffin.
Keyes: Gee, thanks. I sound like a teenager.
Covenant: Dude, cameras! Hi mom!
Master Chief: Great, Covenant on Earth. We're doomed. Let's kill a ton of them.
Marine: Hey, they're blowing up our orbital gun platforms!
Master Chief: So?
Marine: This station is an orbital gun platform.
Master Chief: Oh.
Cortana: Good thing you found that bomb on time.
Master Chief: I have a crazy idea.
Cortana: I'm suicidal too. Let's go for it.
Master Chief: Admiral, I'm gonna drag this bomb into space, fall into a colossal enemy ship, then kick it into its reactor and fall out before it explodes dramatically.
Admiral: I don't see what can go wrong. Go for it.
Master Chief: Ow.
Johnson: Hey, he even picked our ship to land on after all that grandstanding.
Keyes: Let's go down to where the Covenant landed.
Master Chief: Why do I have to get up from a crash every time I land on a planet?
Johnson: No time to waste, you have to kill lots of aliens.
Master Chief: Done. I even blew up that huge Scarab mobile laser platform thing.
Keyes: Good! Let's go after their main ship, it's leaving.
Keyes: I'm a commander too, so I'm both pretty and in charge! I'm just like my daddy, except too hot to be killed off.
Main Alien Ship: I'll just jump to hyperspace inside this city.
Keyes: Dude, that's gonna rip everything apart! Quick, let's slip next to it and follow it!
City: NNNNOOOO! *BOOOM*
Prophet: We're frail and unable to even walk, yet you revere and obey us. Way cool.
Elite: You wanted to see me?
Prophet: Yes. You were in charge of the fleet we sent to kill all the humans, right?
Elite: Yes, but--
Prophet: And you followed them to Halo, and then you watched them blow it up.
Elite: But the Flood--
Prophet: So you're obviously a heretic and must be executed. Take him away.
Elite: Thanks for the painful branding and public humiliation. Wanna kick me while I'm down, too?
Prophet: No, now that we're alone we three oracles thought we'd make you the next Arbiter.
Arbiter: But... that's a great honor! Arbiters are the heroes of our Covenant! They're sent into... horribly suicidal missions...
Prophet: Yup. You get to kill our enemies and we get a corpse. Everybody wins!
Arbiter: I'm just like the Master Chief, except I can turn invisible for ten seconds at a time! Let's kill other Grunts and Elites who dress differently and follow a different god. God they're hard to tell apart.
Friendly Elite: Ow, what the hell?
Arbiter: See? Sorry.
Heretic Leader: Damn you're persistent.
Arbiter: I can load my last checkpoint when I die. Hey, that's...
Monitor: Remember me? I survived the Halo explosion too! I told this guy all I know because he knows how to listen.
Heretic: The prophets lied to us! The Great Journey they tell us the Halos will take us on is nothing but a--DISTRACTION! *ZAPZAP*
Arbiter: No fair! Now I have to kill you.
Arbiter: Just like this.
Monitor: Too bad. Aiiee!
Brute Chief Tartarus: Yoink. Let's go back.
Keyes: Where are we? ...wait, is that--
Cortana: That's another Halo. Right beyond the buildings and highway parts we took with us when we jumped to hyperspace.
Keyes: That other ship landed on it. Let's follow it. Master Chief, drop in with some soldiers and see what's up.
Master Chief: I guess.
Master Chief: Genocide complete. Hey, a temple.
Cortana: Let's go inside. If this is like the last Halo, that must be the control room.
Keyes: I'll go get the key!
Cortana: Good idea. Let's let history repeat itself horribly.
Master Chief: Found the prophet of Truth, one of the three Covenant bigwigs. Want me to hijack his floating chair and punch his face in?
Master Chief: Done.
Cortana: Hey, look up. Fifteen gazillion Covenant ship and a flying goddamn city just hyperspaced in. Let's leave.
Temple: Now's a good time to explode dramatically.
Master Chief: Good thing there's all this water.
Master Chief: Time to sink like a brick!
Tentacles: We'll just hold onto you and drag you into the darkness.
Prophet: Well, we're down to two prophets now. Since the Elites sort of messed up and let the first one die, we'll replace you all with Brutes. They'll do the job better.
Arbiter: That sounds like it'll suck for us.
Prophet: Nah, you guys will be fine. We found another Halo, by the way. Go find the index that'll turn it on. Then we can go on the Great Journey!
Arbiter: Oh no, not the Library! I saw the first game, this area's gonna suck!
Library: Come on, you just need to go to my core and get the index. Nothing bad, repetitive or filled with zombies is gonna happen!
Library: I lied.
Arbiter: You caulksucker.
Keyes: Hey, key! Oh no, gaping chasm!
Johnson: You know, your father never asked me for help, either. Lemme save you from certain death.
Arbiter: Hi, I'm certain death.
Arbiter: I'm a good guy, though. Haven't killed a human yet. I'll just knock you out and grab the girl.
Johnson: Alright. And by that I mean OW!
Arbiter: Got the girl, go me.
Brute Chief Tartarus: Got the girl, go ME.
Arbiter: Hey, my job!
Tartarus: Nope, mine. Me and my brute friends will kill you now.
Arbiter: When the prophets hear about this, they'll kill YOU.
Tartarus: Kill me? They ordered me to do it! I'll just push you into this gaping chasm.
Huge Hulking Plant That Talks: I'm the gravemind. I'm the brain of the Flood. Boy it's been boring all these years waiting for life to return so I could zombify it.
Master Chief: Whatever, I've seen worse.
Arbiter: Demon! What are you doing here too?
Other Monitor: So many people in this creepy underwater cave!
Gravemind: So here's the deal: the Great Journey doesn't kill people, Halos kill people. So we're all pals here and we want to stop it. I'll send each of you to where I think the index is so you can get it and prevent a boo-boo. Teleport power!
Master Chief: Crash a major Covenant conference, check. Watch the Elites rebel and lead the Covenant into a civil war, check. Get backstabbed by the Gravemind who used this diversion to invade the flying Covenant city, check.
Cortana: Told you.
Master Chief: Shut up. Wonder what the other guy's up to.
Arbiter: The Elites are being killed off by the Brutes? REVENGE TIME!
Elites: Hey, let's team up!
Arbiter: Good idea. Okay, we've killed off a lot of them. What now?
Elites: Tartarus is headed for that big control room thing. Let's go crack his skull.
Arbiter: Sounds good.
Master Chief: Okay, that's another prophet killed. Just one left.
Cortana: He's headed for that thing in the distance... it's a huge Forerunner ship they've been using to power this entire flying city. He's gonna escape on it! Okay, leave me here. I'll link up with Keyes' ship that just crashed in here so I can blow it up like we did for the first Halo if things go bad.
Master Chief: Okay, I'll be back.
Cortana: Don't make a girl a promise you can't keep.
Master Chief: Hitchin' a ride!
Forerunner Ship: Off to adventure!
Arbiter: What a scenic route we've taken. Let's free some of our Elite friends.
Johnson: Hey, there goes the lock on my jail cell too! I'll just take control of this Scarab mobile laser platform.
Arbiter: Why you little!
Johnson: Calm down, let's team up. I'll blow the control room open so you can go in there and kill the big baddie.
Arbiter: Okay, deal.
Tartarus: We'll accompany the prophets into the Great Journey, not you stupid Elites!
Arbiter: Sigh, overzealous deluded assholes. Let's kill you and stop you.
Tartarus: Or so you think! Thanks to this weakling girl, I've just activated the ring! Halo will fulfill the prophecy!
Arbiter: Let's kill you anyway.
Keyes: Where's the reset button? Oh, I'll just pull the plug. Yoink! Got the index back.
Keyes: ...what was that?
Monitor: If a Halo is activated but is stopped before it can blow the galaxy to smithereens, it sends out a signal. Now all the Halos of the galaxy are on standby mode, ready to be remotely activated!
Arbiter: Where can they be activated?
Monitor: Where? You're the Covenant, you should know. From the Ark.
Keyes: And where's that?
Earth: Here I am, looming into view!
Forerunner Ship: Here I am, loo-- hey, you stole my line!
Human Forces: Crap, a ship! Let's blow it up!
Master Chief: Not so fast, I'm on it.
Admiral: What are you doing there?!
Master Chief: I'm finishing this fight.
Credits: Time to roll.
Player: Son of a BITCH!