So. Reach. For a while, humans managed to keep the Covenant at bay because of the Cole Protocol, a protocol created by a guy named Cole. Basically, if you’re in a screwed ship, then you deleted the navigation databases and AI. Completely. Totally. Like you don’t want someone to find your hidden porn folder in C:\\Program Files\RandomApplication kind of totally. But then they found Reach’s location. Because Captain Keyes downloaded some porn that had a virus. Or because at the end of a battle the Covenant put a tracker on his ship as he left. Wow. All that hard work by EVERYONE ELSE and all for nothing.
Reach is essentially one giant Pentagon: it is THE military base and headquarters for the UNSC, the training ground for ODSTs and SPARTAN-IIs, and defended by 20 super-MAC cannons in orbit. Also, Keyes cost humanity its best shot at ending the war thus far. Master Chief was just about to leave with ALL the remaining SPARTAN-IIs to try and hijack a Covenant ship, fly it to their mobile homeworld High Charity, kidnap their leaders, and force a truce. But then, that would be too easy, wouldn’t it? So the Covenant show up. Big time.
Humans lost the space battle quickly enough, but the land battle took longer, given that the planet is one giant army and the Covenant came looking for Forerunner artifacts, so they couldn’t glass the entire planet. A group of SPARTAN-IIIs and one SPARTAN-II, Noble Team, are sent to get a vital asset, the smart AI Cortana, from Dr. Catherine Halsey, and deliver it to Captain Keyes’ ship, The Pillar of Autumn. The entire team dies but the mission is accomplished. The Autumn escapes, making a blind jump into Slipspace (FTL) and ends up discovering Installation 04, one of the Halo rings.
Back on Reach, another team consisting of SPARTAN-IIs is tasked with finding Dr. Halsey and evacuating her. They journey deep underground, with Covenant in pursuit, losing several squad members and uncovering a Forerunner shard. They are miraculously rescued by another SPARTAN-II squad and reunite with Cortana and the Master Chief. Where did they come from? Well…
After accidentally discovering one of the Halos, the Pillar is attacked by pursuing Covenant ships. It crashes on the ring surface, and Master Chief discovers the Flood, which were accidentally released by the Covenant looking for relics, which have also taken Keyes. He is persuaded by Monitor 343 Guilty Spark, the overseer robot, to activate the Halo to contain the Flood. He almost does, not knowing how it actually does this, but is stopped by Cortana. They escape from Halo by finding a bomber in the Pillar, and overload the Pillar’s reactors, destroying the Halo entirely. He finds some other survivors in the debris field, and they hijack a Covenant flagship, which they take back to Reach, hence the rescue above. Also, Cortana finds out the Covenant now know the location of Earth. Oh SH#T. Also, they commandeer and reactivate a disabled human ship.
Well, to make some admittedly pretty sour lemonade, the team take down the bulk of the invasion fleet. How? First, the crystal discovered on Reach caused some really trippy Slipspace battle which shouldn’t have been physically possible, so some Marine, pissed that his girlfriend died, blows it up with himself. Next, they find the Covenant’s mobile HQ, and set the reactors to detonate. Then, they take the flagship they have and crash it into the station, telling the Covenant they have the crystal onboard. This draws all the ships more tightly into the blast zone. Only two guys are on the hijacked ship, the rest are watching safely from the human ship, and the explosion destroys over 500 covenant ships. This allows the survivors to return to Earth with a warning.
The Prophets are pretty understandably very mad that one of the Sacred Rings was destroyed, and they order the Elite commander of their forces there to be branded with the Mark of Shame and stripped of his rank. He is offered a second chance by becoming Arbiter, essentially a guaranteed suicide with honor, and after being given a fancy ne..urh... incredibly old set of armor, he is sent to kill the Leader of a new heretical Covenant splinter group. The leader of this splinter, who is under the tutelage of Guilty Spark, now understands the Halos for what they actually are, but the Arbiter kills him anyways and takes Guilty Spark.
Meanwhile Earth is invaded, with the action mostly focused on East Africa, because the portal to the Ark buried there is a giant homing beacon for the Covenant. A group of ODSTs land in New Mombasa, Kenya to try and erase the detailed information about the site to delay the Covenant, and acquire a defecting Engineer in the process, which gives the humans very valuable insight into the site.
However, MC and Co. are giving chase to the cowardly Prophet of Regret, and they discover another Halo. However this one has already been taken over by the Flood, which have gathered enough consciousness to form a sentient presence, known as the Gravemind. The Arbiter also arrives, but he is looking to start the ring and redeem himself. Both are captured by the Gravemind, who reveals the true nature of the ring, and tells the both of them to stop the Brutes and their leader Tartarus, who have replaced and usurped the Elites in a huge political and military coup. They do this, but Cortana is left behind as MC escapes back to Earth in a Forerunner ship parked on the ring.
Master Chief jumps out of the Forerunner ship and crashes to Earth from orbit like Felix Baumgartner sans parachute and lives, even without the convenient haybale that somehow makes the physics work. He meets up with the Arbiter again, and they go to destroy the Covenant AA overlooking the now excavated portal to the Ark, so that the handful of human ships left can launch a surprise attack. Then a ship of Flood show up, and inside MC finds a recording of Cortana warning that the Gravemind is coming with an army of Flood. MC, Arby, and the Elite fleet pursue the Brute fleet inside the now-activated portal, and discover the Ark. They get to the control room and stop the Prophet from activating all the Halos and kill him. Then the Gravemind shows up in High Charity, and the duo overload the reactors on it, destroying it, and MC snags Cortana back in the process. They realize that the Ark is almost done building a replacement Installation 04 because MC destroyed the original, and they fire it inside the Ark to finish off the Flood here entirely. They get through the collapsing portal, but it shorts out halfway, so the Arbiter on the front end of their ship Forward unto Dawn makes it to Earth, but the Chief in the back ends up floating by Requiem. With a broken ship and no way to get back to Earth, Chief hibernates for a few years while waiting for rescue.
The Covenant are defeated, the Prophets gone, the Brutes back to fighting each other, and the Elites and humans are at peace. But of course, nothing is fine and dandy. Although formally the Arbiter and the UNSC have declared a state of peace, factions on both sides are agitating for conflict again. Elite religious fundamentalists who still believe the Forerunners are gods are furious at the Arbiter for his apparent softness and blind belief the humans will simply leave them be. In fact, they are right, because super-secret ONI already has a devious plan to ignite civil war between the Elites.
ONI begins using covert teams to funnel weapons to the religious group, who are planning to launch a rebellion and coup against the Arbiter, and will take whatever they can get. Also, the UNSC persuades the Elites to allow a researcher to land on their homeworld and investigate Forerunner structures, which the Arbiter allows, which REALLY infuriates the religious group. The researcher discovers many different glyphs referring to ‘do not’ and ‘Didact’, as well as the elaborate portal system. But the resulting anger he causes makes the religious nuts rebel prematurely, so they are underprepared, and the Arbiter takes the upper hand. A quickly quashed rebellion is no good, so a secret ONI ship takes out several of the Arbiter’s ships to even out the fight, and an extraction team rescues the researcher.
Oh, and we have a giant-ass ship now called the Infinity that we were apparently building somewhere (?) during all that last ditch fighting mentioned above. I know we’re pretty quick on the rebound, but in five years we’ve gone from literally no one and nothing left and Earth being completely taken over to doing great and building ships bigger than the Covenant’s. I heard that Germany just finished paying its war reparations in Oct. 2011… from World War I. I guess they had to hurry things up or else Master Chief would have needed a walker for the new games. And I’m not referring to the Mantis. Also, now we’re taking Spartans to the power of 4. Now that there’s no wartime fear, we can bathe in the guilt of kidnapping little kids and performing maximally invasive surgery on them, so SPARTAN-IVs are going to be made from grown-up volunteers (as well as all the remaining Spartan IIs and IIIs).
The leader of the religious rebels escapes and is able to find some of the glyphs that show the Didact absolutely hates humans and is located on some place called Requiem, and thinks he would be a GREAT ally. So he goes about trying to find him. Which brings us to…
The Here and Now
(You are now ready to take on Halo 4, with all the knowledge you would possibly need to have a fulfilling, enriching grunt shooting experience. However, in case you were confused by some aspects of Halo 4, or just like our writing style, read on at your own risk.)
Cortana’s had nothing to do for a while, so she’s slowly been fragmenting and corrupting all this time, like your computer does after you use it for a long time. But the arrival of that Elite’s fleets in front of Requiem trips an alarm, and she wakes up Chief, and all of them, Covenant and human alike, get sucked into the gravity well of the opening portal which takes them inside Requiem. (remember, Requiem is a Shield World) Infinity, responding to Chief's distress call, also happens to be nearby and gets sucked in as well.
Master Chief is tricked into releasing the Didact from his prison, and the newly freed Forerunner battlemaster traps the Infinity on the planet, but MC and his new deluxe model Spartan friends (who are conveniently stored on board the Infinity) scare the Didact and clear away the defenses so Infinity can leave. Chief actually wants them to stay because he needs help to defeat the Didact and eliminate the Composer, but the Captain hightails it out, leaving the Chief to do EVERYTHING. AGAIN. Also, the ghost of the Librarian shows up and reveals that it was apparently her plan all along that MC would be created, and that it was all thanks to her perfect planning. Wow. Could you be more boastful about it? She does do him a solid by making him immune to the Composer though.
So he follows the Didact out to Installation 03, because the Composer is located on a human research station embedded in an asteroid close by. Didact steals the Composer and runs to Earth, intent on finishing what he started over 100 millennia ago. But never fear, the Chief is here, and he stops the Didact by throwing a nuke into the Didact's ship. However, Cortana is forced to sacrifice herself to save Chief and make sure the resulting nuclear blast doesn't kill him too.