The Codex

The Praetor, a high-ranking Covenant general, is brought before the Council to be interrogated after he rushed in to investigate a signal he believed was coming from the ancient Forerunner structure known as The Codex. His failure to alert the proper religious authorities made him the subject of great suspicion, but he is able to prove himself innocent of malicious intent. Due to his ledgendary skill, he is given command of the invasion of the planet Ariaos II and the capture of The Codex. Meanwhile, the Spartans detect the Covenant invasion force en route, and begin to make preparations for the defense of the planet.

The Praetor, from the flagship of the Covenant fleet orbiting the planet, orders the invasion to begin. The plan calls for a Special Operations team to secure the cave in which the Codex is located, and then for a full invasion of the planet once the Codex is declared safe. Meanwhile, on the surface, Green Team is guarding the cave housing the alien structure when they are ambushed by the SpecOps Elites. After a quick but bloody struggle, Green 2 is ordered to flee from the cave to get re-enforcements. He protests, wishing to stay with his team, but is forced to follow orders. He makes his way out of the cave, fights through a nearby city, captures a Covenant Banshee, and heads back to Delta Base.

The Praetor moves his command headquarters into the Olympia cave sytem. Soon after settling in, he is alerted to the presence of a very high-ranking Covenant religious official: the Cleric. A member of the religious elite, the Cleric proves himself to be a magnanimous and complimentary person, until his authority is questioned. When the Praetor introduces the Cleric to the Special Operations Commander, Anda Sofadee, the Cleric directly insults her competence based on that fact that she is a female. This eruption of anger on the part of the Cleric almost leads to a brawl between the Cleric and the SpecOps Commander, but the Praetor seperates them. When the SpecOps Commander is dismissed, though, the Cleric turns his wrath against the Praetor and tells him in no uncertain terms that the Cleric will be watching his every move. After a cold but wrathful quarrel, the two seperate and the Cleric orders the Seraphim, his personal gaurd, to keep an eye on the Praetor. The stage is set for a power struggle within the Covenant hierarchy.

Back at Delta Base, the Chief and Red Team prepare to join the fight against the Covenant. Green 2 makes his way back to the base in the captured Banshee, but not before almost being shot out of the sky by Blue Team. As everyone arrives at the base, Jack comes out to meet Candy, and they have a less than warm exchange. Before they can really lay into each other, though, they are called into the Briefing Room to talk to Lykurgus and the Chief. The four of them discuss their options, and decide to attempt encoding a message into the energy bursts sent out by the Codex in an effort to contact Earth. Blue Team is given the mission, while Red Team is ordered to hang back and help plan future strategy against the Covenant.

The Praetor learns of Green 2's position, and thus the location of Delta Base, by tracking the captured Banshee. He orders an expedition be sent under Erda Renadee, the Battlefield Commander, to destroy the Spartan base. Meanwhile, Blue Team arrives at the dish at the top of the Codex, with a mission to encode a signal into the bursts sent out by the structure. Although they sense that something is wrong, they cannot find any Elites in the entire complex. The Elites are cloaked, setting up a checkmate move with which they can eliminate all of the Spartans at once, and thus minimize the casualties. Finally, though, Blues 1 and 2 manage to find two uncloaked Elites and reveal the potential ambush. An alarm is raised, and the Spartans prepare for battle.

As Blue 2 alerts the other Spartans to the presence of the Elites, the trap is sprung. Hordes of Covenant rush the Humans, who quickly fall back into a corner. As Blue Team prepares to make its last stand, they radio Delta Base for reenforcements, only to learn that Delta Base is itself under attack by a massive Covenant army. After a long bombardment, the Spartans at Delta Base retaliate with a volley of rockets and prepare to defend the base.

As waves of Elites assault the base, the Spartans inside are forced to fall back and relinquish the dock. Jack, who had been guarding the dock, looks out into the Covenant army and sees a Red Officer commanding the nearby forces. He quickly decides to eliminate that commanding officer, and starts a death-defying rampage across the field to get to him. After killing him, though, Jack is cornered by Covenant artillery and infantry. But just before they can fire, Blue Team miraculously appears in the Warthogs and slices through the Covenant lines, throwing the Elites into disarray.

The Praetor delivers a welcome address to the Foreman and his Engineers, who have come to excavate the rest of the Codex and attempt to activate it. After his speech, the Praetor notices several of the Cleric's Seraphim guarding a door. He dispatches the Special Operations Commander to investigate, but she is blocked when the Captain of the Seraphim arrives on the scene. When she returns with a lance of her Special Operations Elites, she finds the room empty and abandoned. However, unbeknownst to her, the Cleric had already ordered that the contents of that room be brought before him for interrogation. It is a prisoner: a Spartan known as Green 4.

Green 2 goes on a walk alone out in the field near Delta Base, remembering the day his whole team was killed. When asked about what he is thinking by Jack, he admits that he is having regrets about leaving his team. In the meantime, Lykurgus intercepts a Covenant signal hinting at a Human prisoner being held in the Olympia caves, and the decision is made to rescue him.

After sneaking into the cave through an abandoned mineshaft, the Spartans get into position and launch the attack. They rescue Green 4 from his cell and fight their way out of the cave, but Green 2 sacrifices his life to buy them time so they can escape.

The Praetor and the Cleric are fighting again, this time about whose fault it was that the prisoner escaped. The Foreman announces that he has found a potential entrance through a ventilation shaft, but the Cleric does not allow the blasting that would be required to open the tunnel. The Cleric then makes a chilling remark: if the Praetor does not act quickly, the Cleric will arrest him and take over the operations around the Codex.

Responding to the Spartans' call for help, a small flotilla of UNSC ships appears in orbit. They are quickly destroyed by the Covenant fleet, but not before many ODSTs make it to the surface alive. Meanwhile, the Spartans return to Delta Base and find it occupied by Erda Renadee's Elites, and are forced to find a new home. After hooking up with the ODSTs and their leader, Sergeant Henderson, who were holed up in the wreckage of their destroyed ship, the Humans make their way to a remote mountain fortress called Mt Jefferson.

Erda Renadee follows the Spartans to the crash site of the Human starship, killing the last few ODSTs left there. The Spartans arrive at Mt Jefferson and start to get set up, but before they know it, Erda's army appears outside the gates and begins the seige of Mt Jefferson.

The Covenant are repelling all the Human attempts to destroy their tanks with anti-rocket guns. The situation is a stand-off, until the Covenant send out their Ambassador to try to negotiate the Humans' surrender. Sergeant Henderson does not take kindly to this and shoots the Ambassador in the face, thereby bringing the full retaliatory strike down upon the Humans. The battle is joined...

The Humans are holding the fortress against the relentless attacks by the Covenant, but Erda's forces tunnel under the wall and send several cloaked Elites into the fortress to open the gate. Jack realizes the plan, but is too late to stop the Elites from slaughtering the wounded Humans and opening the gate. Elites pour into Mt Jefferson, and Erda Renadee personally joins the fight, killing Sergeant Henderson with his own blade. He then sees Jack and immediately recognizes him as the reason for Erda's failure at Delta Base. Driven into a blood-rage, Erda attacks Jack and is killed. As Elites continue to fight through the open gate, the Chief is forced to order an evacuation of the fortress. The Humans flee through the tunnels in the back of the base, and some drive the Warthogs straight out through the Covenant army. They leave a little surprise behind them, though: a bomb which destroys Erda's army.

The Cleric chastises the Praetor about his loss at Mt Jefferson, then meets the Foreman, who is on his way to meet with the Praetor. The Foreman says that they have found an entrance to the Codex, and they only need to summon the Praeceptor to enter. The Cleric asks the Foreman to not tell the Praetor, but the Foreman refuses to conspire against his commanding officer. The Cleric then tells his Seraphim to kill the Foreman. However, Anda Sofadee hears of this plot and the Praetor orders her to have her Special Operations Elites shadow the Foreman and protect him. The Foreman begins to notice this, though, and thinks that the Praetor is trying to kill him. He goes to the Cleric for help, and is executed in secret.

The Seraphim arrive at the Temple of the Holy Praeceptor. They are shadowed by ODSTs, who follow them inside the temple. Inside, they are slaughtered by the Seraphim, who then begin the activation of the altar and the summoning of the Praeceptor. Another group of ODSTs enter just in time to witness the Captain of the Seraphim become the Praeceptor himself. He then levitates up into the air and destroys the ODSTs with a huge blast of energy. The remaining Humans outside the Temple are no match as the Seraphim begin their journey back to the Codex.

The Chief examines the dead bodies of the ODSTs, and the Praetor realizes that the Humans are headed for the Codex. Lykurgus learns the function of the Codex: to activate the Halos and destroy all sentient life in the galaxy. Realizing the incredble danger that the Codex represents, the Humans decide to destroy it. At the same time, the Praetor and his troops prepare to defend it to the last man. The stage is set for the final battle for the future of the Codex.

The Praetor goes to personally command the defense of the city surrounding the Codex, and establishes the battle lines. Jack shows a little bit of tenderness toward Candy, but then rushes off into battle as the fighting begins. A hard fight begins through the city toward the Codex, but the Praetor is forced to return to the cave when he is told that the Cleric is about to enter the Codex without him. After an attempt to arrest the Cleric, the Praeceptor destroys the Praetor's warriors and arrests the Praetor. The Cleric enters the Codex at last, with the Praetor as his prisoner.

The Cleric enters the Great Chamber and is introduced to the Guardian. Meanwhile, Anda Sofadee hears of the Praetor's arrest and takes control of the Covenant Army, with the intention of resuing the Praetor and killing the Cleric. The Humans continue to fight into the caves, and sneak into the Codex through the ventilation shaft discovered by the Foreman. Three sides of a battle hurdle toward each other as The Codex reaches its stunning finale!