First Battle of High Charity

The First Battle of High Charity was a large battle for the control of the Covenant capital world High Charity between the Covenant Separatists, the Covenant Loyalists, limited United Nations Space Command forces, and later, the Flood. The battle marked several significant events: The start of the Covenant Civil War, Spartan John-117's chase of the Prophet of Truth and the Flood Invasion of High Charity.

The Fracturing of the Covenant
The Battle of High Charity was an inevitable battle. With the Brutes, who directly competed with the Elites, slowly gaining the favor of the Prophets, it was only a matter of time before the Elites were overthrown and open warfare began between the two parties. However, multiple events helped bring about the battle.

Recent failures of the Elites leading up to the battle (including the loss of Installation 04, the annihilation of the Unyielding Hierophant and the fleet around her, and the assassination of the Prophet of Regret by the UNSC) damaged the reputation of the Elites and further empowered and emboldened the Brutes. These events spurred the Changing of the Guard, giving the Brutes the duty of protecting the Prophets - a job traditionally held by the Elites and further damaged their reputation and position within the Covenant.

Battle of Installation 05
However, while the eventuality of the Battle of High Charity was a foregone conclusion, its scale was not. The Prophet of Regret's wayward mission to Earth brought High Charity, Spartan-117 and In Amber Clad near Installation 05. With the Gravemind already released and plotting its way off of the Halo, this would set the tables for the invasion by both the Flood and the legendary "Demon".

An attempt to kill Spartan-117 from orbit had failed and instead threw him into the clutches of the Gravemind. It would be Tartarus, however, who put the final pieces of the puzzle into place - some of them inadvertently. After the Arbiter successfully acquired the Index from the Library, Tartarus attempted to execute him by firing a burst from his Gravity Hammer at the Arbiter and knocking him into the depths of the Library. He then took the Index and UNSC Commander Miranda Keyes and Sergeant Major Avery Johnson as prisoners back to High Charity where the Prophets of Truth and Mercy waited.

Gravemind
The Arbiter, however, would not be slain there. The Gravemind had other plans for him along with Spartan-117. The Index was now in the hands of the Covenant, and as ignorant as they might be to the true purpose of the Halos, they were fully intent on firing the Halos - an act that would prove fatal to the Gravemind should it happen. As such, he knew that the Halos must not be fired, and for that he brought two of the greatest warriors and the ones most likely to stop the Halos. He sent Spartan-117 to High Charity and the Arbiter to the Halo's Control Room - the two most likely places for the Index to be. He then prepared to bring the other part of his plan into action - the invasion of High Charity.

Master Chief's Entrance
The battle began in the Council Chamber. The Prophet of Truth (with the Prophet of Mercy at his side) was giving a speech to the Covenant acknowledging the release of the Flood and announcing Tartarus' successful acquirement of the Sacred Icon. As he drew his speech to a close, Spartan-117 was teleported into the room, standing right beside the Grunt who was filming the speech. He acquired the Grunt's weapon and aimed it at the Prophets, but the Brutes covered the Prophets so they could escape.

Once he secured the Council Chamber, Spartan-117 inserted Cortana into High Charity's power grid so she could open the doors to the room. She then opted to remain in High Charity's system as she felt it would provide her the greatest opportunity to aid him. With the Index clearly in the possession of the Prophet of Truth, the Spartan chased after the fleeing Prophet.

Rescue
"Listen up Marines: the Master Chief is hunting a Prophet, and you're going to help him kill it."

- Cortana

Shortly after beginning his hunt, Cortana noted that there were Marine transponders near the Master Chief's position. After raiding the prisons, over half a dozen Marines joined the Spartan in his hunt for the Prophet

Covenant Civil War Begins
"The Elites have failed to protect the Prophets, and in doing so, have put all our lives at risk. Let no warrior forget his oath, 'Thou, in faith, shall keep us safe, whilst we find the Path.' With my blessing, the Brutes now lead our fleets! They ask for your allegiance, and you shall give it."

- Prophet of Truth

Soon after the Marines were rescued, the Prophet of Truth declared that the Brutes were now in charge of the Covenant fleets. The Brutes then instigate a genocide of the Elites, as secretly ordered by Truth. War breaks out on High Charity and the Covenant Civil War begins. As Spartan-117 and his marines moved around High Charity, they bore first-hand witness to the fracturing of the Covenant, sometimes opting to watch as the two sides fought rather than becoming directly involved. The Brutes focused on attacking Elites in the towers of the city, then spread out to the lower levels. The Elites that survived the initial betrayal retreated to the Mausoleum of the Arbiter to make a last stand, supported by many Hunters and Grunts. The causeway leading to the Mausoleum became a battlefield choked with dead from both sides. However, the Brutes were eventually able to push through, and fighting spread to the central chamber of the Mausoleum itself.

The Flood Invade
"Slipspace rupture. It's In Amber Clad! Hailing... No response. She's crashed into another tower ahead of our position. I'll keep trying to make contact, but I'm not registering any human vital signs."

- Cortana

Sometime later, In Amber Clad entered High Charity via Slipspace, flying across the City before crashing into a tower on the other side. Cortana tried to contact the ship but registered no life signs on board. It would be a while before the true nature of In Amber Clad's arrival would be known, for she had been captured by the Flood and it was they who had flown her in. The various short range craft she possessed launched and spread the Flood soldiers throughout the city.

Mercy Falls
In the race to capture the Index, the Spartan lost. The Prophet of Truth made it to his escape craft and handed the Index over to Tartarus. Tartarus prepared to take the Index along with UNSC prisoners Commander Miranda Keyes and Sergeant Major Avery J. Johnson to Installation 05 to activate the Halo.

Before they could leave, however, Flood Infection Forms attacked them. Tartarus and his Brutes tried to defend the Prophets of Truth and Mercy, but one of the Infection Forms got through their screen and landed on Mercy. Tartarus moved to remove the Infection Form, but the Prophet of Truth ordered him to let the Prophet be. Tartarus proceeded down to the surface.

Departure
By the time Spartan-117 had reached the Prophet of Mercy, the Prophet was nearly dead and the Marines he had rescued had similarly fallen. In his interrogation of the Prophet, he discovered that the Prophet of Truth was fleeing towards Earth. Cortana determined that Truth was heading towards the Forerunner ship which stood in the middle of the City.

With the Arbiter still on Installation 05 and Cortana stating that she could detonate In Amber Clad's reactors if it was needed to destroy the Halo installation, the Spartan proceeded to follow the Prophet of Truth and attempt to board his ship before it left. However, Cortana chose that she couldn't trust the failsafe detonation of In Amber Clad to any copy of herself and had to remain behind.

While Cortana tried to stall the launch of the Forerunner ship, the Master Chief moved through the maze of High Charity, fighting Flood and Covenant alike to board the ship. During that time, Cortana realized that the ship was actually the power source for High Charity. In the end, he got on board with mere seconds to spare.

Covenant Civil War
"The Covenant just destroyed two of their own ships. And I'm hearing reports of small arms fire throughout their fleet."

- Cortana

The Battle became the first battle of the Covenant Civil War. Warships around High Charity continued to fight well after the battle on the surface of High Charity itself was over. However, whether the battle's outcome would have any lasting impact on the outcome of the Covenant Civil War is currently unknown. That said, the fact that neither side was able to acquire control of High Charity likely limited any major gains that were to be had.

Tartarus and the Index
Tartarus would eventually make it to the Control Room with Miranda Keyes and begin the firing sequence for Installation 05. However, the Chieftain would eventually fall to the Arbiter and the firing sequence would be aborted, putting all remaining Halo Installations into standby mode.

Prophet of Truth and Spartan-117
The Prophet of Truth and Spartan-117 would eventually reach Earth aboard the Forerunner Ship and participate in the Second Battle of Earth. Upon it's arrival, Lord Hood ordered the ship to be destroyed, but Spartan-117 identified that he was aboard the ship and wanted to finish the fight.

High Charity
The Flood eventually gained full control of High Charity and the Gravemind would take up residence in the fortress. However, the city was disabled with the decoupling of the Forerunner Ship, without power and likely unable to move. Cortana, stranded in High Charity's computer, would be questioned by the Gravemind who turned the city into a massive Flood Hive. Apparently between Halo 2 and 3 the city gets connected to an existing reactor that was probably some sort of back-up and is fully functional once again. In the Second Battle of High Charity the city is destroyed by the Master Chief who blasts the reactor causing it to go critical.