Around the 2500s, Humanity has used their Shaw-Fujikawa Slipspace Drives to conquer a pretty small sphere of space, around about 60 or so planets, I thinks.

Unfortunately, humans being humans, there were many rebellions and space uprisings. As the UNSC was often too slow to deal with this, a special project was begun. The Spartans.

These genetically-engineered humans were really helpful. However, they were all adults recruited from the military, and this meant those amoral scientists couldn't have much fun.

So of course, they got greedy. They snatched healthy young kids from across the UNSC worlds, flash-cloning and brainwashing replacement children. Unfortunately, flash-cloned full humans, unlike mere organs as the process was normally used for, were pretty much imperfect and tended to die in agony after a few years. But who cares, Super Soldiers.

On the super-duper military fleet base of Reach, these kids were heavily modified and experimented upon. This was painful and most of them died. But those that didn't tended to become superhuman, strong and smart with reflexes like Flash after some caffeine. These experiments, tests, and modifications were carried out by one doctor Catherine Halsey, who by the way was used as the brain-scan and body template of Cortana, the famous naked blue AI chick.

 

So anyway, Reach was going grand. On the other end of human space, on a small farming world called Harvest, contact was lost. Oh noes! So the UNSC sent a ship to investigate. Said ship entered the system, reported seeing another purple ship in orbit, and got shot down. Shoot. So of course, the UNSC declare war. the aliens reply with "Your destruction is the will of the Gods, and we are their instruments." Charming. So the Covenant, as the alien army is now know, start glassing (basically burning the surface of a planet in orbit until all the dirt and sand and minerals end up like glass), destroying, and outright wasting every Human planet in their path. While the UNSC marines can take down the aliens on the ground, the minute they get in space, human ships get razed. All the outer colonies fall, and then the inner colonies.

 

To stop this, the human military gathers a HUEG LIEK ECKSBAWKS fleet of all their best ships at Reach. Their strategy is to turtle their way into Covenant space and capture some sort of military leader, to bargain for peace. While doing this, the Spartan IIs, now in their famous MJOLNIR Power Armour, find a mysterious artifact on a nearby planet. The funny symbols on said artifact are realized to be Slipspace codes, and The Master Chief as he is now known heads back to Reach. Unfortunately, the Covenant are already here, having bombed most of the planet to heck and chewing the fleet up like cat-toys. An outdated ship, the Pillar Of Autumn, is told to take Cortana and the Chief onboard and get the heck out of there. After this, the Chain of Command on Reach is wiped out and most of the Chief's Friends die too. This sucks for him cuz they're like brothers and sisters, you know?

 

So anyway, this banged-up ship used a "Blind Jump", however it was secretly decided to use the co-ordinates on the mysterious Artifact. This, of course, brought them to Halo. Halo is this floating artificial Ringworld held in orbit between a gas giant and a moon. Of course, the Covenant is already there, examining the Holy Relic. So, being either courageous or incredibly dumb, the Captain of the Pillar of Autumn, Captain Keyes, charges right in and brings his heavily damaged ship down on a plateau on the Halo. The Master Chief and his AI friend land in some other area, all their fellow Marines in the escape pod dying in the process. After finding a large bridge, some structures and a ginormous tunnel, they begin to believe that something very interesting is going on here. Of particular note is that the control panels seem to be workable to all the humans...somehow.

 

After linking up with the rest of the Marines and surviving crew, they make for a base set up by the Humans called Alpha Base. What a great name. The guy in charge, Major Silva, is a big pain in the neck to the Master Chief and considers his own troops superiour. After a bit of ranting and repairing, Silva finds out that the Captain got himself captured and is locked up on a damaged Covenant ship hanging over a desert canyon. So, in go the Chief and a bunch of Marines, who totally blitz the surprised Covenant forces and rescue him. Along the way, they discover the Covenant talking about the Ringworld, calling it Halo and a "weapon". After the escape, the Captain orders the Chief and Cortana to head for a small island where something called the Silent Cartographer is located. This hectic battle resulted in Cortana learning to location of a place called the Control Room. After letting Captain Keyes know, he mentioned something about a Covenant Weapons cache and drops out of contact. After another fierce battle out of the island, the Chief and Cortana hop on a Dropship flown by their pilot friend Foehammer to travel through a massive underground tunnel network. Cortana reasons this will be very surprisingfor the enemy.

 

At any rate, they arrive in an cavernous room and surprise the Covenant occupational troops. After heading along on foot, the Chief and Cortana come out in a snowy valley and run into surviving human marines from Fireteam Zulu. And they have a tank around here somewhere. Happy Happy Joy Joy! After blasting through a ton of troops and enemy hovercrafts, the Humans arrive at another set of tunnels. After radioing the Fireteam some evac, the Master Chief and his AI continue on ahead.

 

Finally, they arrive at the control room. Again after wasting a small army of troops, the Master Chief enters the HUEG LIEK ECKSBAWKS room and sticks Cortana in the console.(tee hee!) Cortana boasts about how spacious it is in there (snicker!) and informs the Chief that this isn't just a weapon, it's....Wait...What? This can't be right. The ones who built this place, the Forerunners, they called it a Fortress World....to...You have to stop him! You have to stop the Captain! It's not a cache, it's...just go!

 

Dramatiiic.

 

So of course, the Master Chief hops on the Dropship with Foehammer and heads off to the musty swamp where the Captain went. After picking up a shotgun near a crashed human dropship, the Spartan discovers some covenant. Oddly, there don't seem to be any Elite soldiers here, just the usual grunts and jackals. How perplexing. Anyway, the MC hops into an empty gun-turret and mows them down. A quick bodysearch reveals no Elites, as he thought. Mysterious. Anyway, the Chief heads along through the dank, dark swamp, noticing the occasional friendly unit signal on the edge of his motion tracker. So strange. He then caught up to another crashed dropship, this one a Covenant U-Haul. Beyond it lies the facility. It's a big Forerunner bunker with huge floodlights (hint hint), and a bunch of Covenant are running away from it after some human rounds are fired in the distance. Friends! thinks the Master Chief. Inside, after picking up some ammo, the Chief rides down the elevator into a set of huge rooms. This massive set of identical galleries and halls start to get monotonous...until The chief passes a room filled to the brim with blood and alien bodies. Hmm.

 

The walk through the sometimes-empty, sometimes bloody and full of corpses rooms continues, until the Chief encounters a lone human marine in the middle of a bloody hallway. He mutters a bit. He also tells the Chief to "find your own hiding place!" and claims to be able to "hear" them when the Chief approaches. Creepy. After leaving the poor dude in the fetal position, the Chief finally makes it to the end of the facility. He discovers some blood, human bullet casings everywhere, and hears some mysterious slurpy sounds as he approaches a Door that has been hacked by human hands. He opens the door.

 

A dead marine who was pressed against the door falls into his arms. In full alert mode, the Chief drags the body in and shuts the door. The room is full of blood and bullet casings, but no bodies. Curiouser and Curiouser. He then finds a helmet with a nasty hole through the top, and extracts a video recording. After fast-forwarding to the arrival of Key's squad at the facility. He sees the troops get off into the swamp while the Sergeant listens to rock music, and he sees them discover a covenant body with the insides ripped out. He then sees them enter the room the Chief was now in. He then watches as hundreds of bulbous and bouncy little creatures swarm the marines. Though fragile, they bring down most of the Marines with horrid little tentacles that enter through exposed skin. End recording. The Chief watches with horror in the present as the horrors return. People, meet the Flood.

 

After barely fighting off the swarms, the chief returns to the door only to be swarmed by a bunch of reanimated corpses. Their spastic fighting style, incredible speed and ability to use weapons makes them a tough opponent. Of course, they're corpses, so they're kinda fragile. After narrowly escaping, the Master Chief and some Marines he finds topside fight their way to a long metal tower rising out of the mud. The Chief is telephoned inside the thing, and meets 343 Guilty Spark, the AI monitor of the Halo Ring. After his weapons are unable to harm the machine, the Chief decides to play along with the crazy little AI, who refers to him as the "Reclaimer". Together they travel through a massive underground Floot-Infested facility called the Library, where at the very end they discover a small floating object called the Index. The Chief takes it as the Monitor explains that it is required to activate Halo and destroy the Flood. They are then teleported back to the control room.

 

Once there, Cortana reveals that the Halo just doesn't work that way. the ring doesn't kill the Flood. it kills their food. *shock!*

 

The ring basically brainexplodes all intelligent life in the galaxy, in tandem with a bunch of other rings scattered around the Milky Way.

 

So of course, the Moniter orders his killbots to wipe out the traitourous Reclaimer, and the Chief and Cortana escape through the valley, trying to destroy a bunch of Phase Pulse Generators along the way. these are basically big amplifiers. With that out of the way, Cortana report to Silva that they're gonna blow the Pillar Of Autumn and destroy the ring with a big Asplosion. Silva, with his hands full, agrees, and it is decided that Cortana will retrieve the Captain and get him and his command codes to activate the Self-Destruct. they find out that he's actually inside the downed Covenant ship from before, witch is being raided by Flood. So, the Chief will arrive, cause mayhem, rescue the captain, and then head for the Pillar. Then, Silva will take remaining troops and take over the weakened Covenant ship and escape.

 

Cortana teleports the MC onto the damaged ship, the Truth and Reconciliation. After going down a few corridors and hearing some pained words from their Captain over the radio, they then fall out of a massive hole in the ship and land in a pool or Reactor Coolant. Anyway, they make their way through the flood and Covenant fighting each other like beasts, and manage to board the ship. In side, after evading a swarm of Spec-Ops Covenant, they find the Captain... Only to see that he's become a big flood brain thing. Of course, this doesn't phase our Spartan, who then punches it in the head and retrieves the Command implants. After fighting through more Covenant reinforcements, they steal a Banshee Fighter and head off to the crashed Pillar Of Autumn.

 

By the way, the the Humans did manage to take the Covenant ship. Unfortunately, one of the power-hungry commander's subordinates found out that he was bringing the virulent Flood along with him on the ship as spoils of war. Realizing what she had to do, the young woman calmly set of a grenade in the Fusion Reactor, causing it to lose control and destroy the ship, the humans with it. So at this point the only humans left are the Dropship Pilot, the Chief, and Cortana.

 

At the Pillar, the vessel of course full of Covenant troops, Flood, and Sentinal drones, the Chief and Cortana manage to reach the bridge. They set the time and begin to head to an escape pod so they can meet up with Foehammer. Unfortunately the Monitor catches them, and disables the countdown manually from the engine room. As Cortana bewails her lack of ideas, the Chief gets one: "What about if I chuck some grenades into the Reactor to destroy the Magnetic Containment fields?"

 

This works. After destroying the Engine's safeguards and chasing off the monitor, they've got about 15 minutes to drive down the top of the ship through the hangars and vehicle bays to reach Foehammer's Dropship. And begins the final stretch. As they burn rubber in the Warthog jeep, the Chief basically runs over every kind enemy in the game. As the ship begisn to go critical, they reach Foehammer's pickup spot..only for her to be shot down. Shoot.

 

But wait! There's a fighter still docked at the end of the ship! The pedal is put to the medal and they flip the warthog under heavy fire and chased by thousands of Flood, leap onto the ship, start the engines, and escape as Halo's structure comes apart. the Ring is destroyed...

 

Cortana: "Fancy a look?"

 

{The Master Chief rises from his chair and moves to one of the Longsword's windows. Halo has broken into a few dozen large fragments, all of which are slowly spinning away from each other. As the Chief watches, one massive fragment comes swiftly from the far side of the ring and collides with another, closer one, splitting it in half, and the two go spinning off in a giant gout of fire and debris. Silent explosions spread throughout Halo.}

Master Chief: (braces himself against the frame of the Longsword's cockpit) "(quietly) Did anyone else make it?"

 

Cortana: "Scanning." (Pause) "Just ... dust and echoes. We are all that's left."

 

(The Master Chief shakes his head and moves back to his seat)

Cortana: "(hesitant) We did what we had to do ... for Earth. An entire Covenant armada obliterated, and the Flood ... we had no choice. Halo ... It's finished."

 

Master Chief: "No." (The Longsword is alone in space, and through the window the Master Chief reaching up to unclip his helmet from the rest of his suit, camera moves up, the frame of the Longsword blocks the view from Master Chief's face) "I think we're just getting started."

 

{ The camera tracks the Longsword for a few a moments, Basis looming large in the background, before panning to focus on a large spiral galaxy hanging in the sky, an ornament emblazoned across the heavens. A few final, dark notes of a cello play, and everything fades}

 

And at the end of the Credits, floating in Space, is the Monitor.

 

As an aside, I haven't played that game in YEARS. Basically I used a Wikia for a few tricky names, but that's all.