Raid on the Threshold gas mine
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During the Ninth Age of Reclamation the forces of the Covenant, under the command of Arbiter Thel 'Vadamee and Special Operations Commander Rtas 'Vadumee, launched a raid against the heretical movement led by Sesa 'Refumee on a Forerunner gas mine over the planet Threshold, near the ruins of Halo Installation 04. The Covenant force's objective was to assassinate 'Refumee, whom the Hierarchs saw as a threat and offense to the Covenant.
During the Battle of Installation 04, the Prophet of Stewardship sent a team led by Sesa 'Refumee and Loka 'Bandolee to the gas mine to recover Forerunner artifacts. When the ring was destroyed by SPARTAN John-117, this artifact retrieval team survived aboard the mine. Some time later, 343 Guilty Spark, the monitor of Installation 04, arrived at the gas mine. The monitor, whom the Covenant forces regarded as an "Oracle", informed them of the true nature of the Halo Array: the rings would not propel the Covenant's faithful along the Great Journey, but would instead kill all sentient life in the galaxy. This inspired 'Refumee and most, if not all the retrieval team, to refute the Great Journey. They soon began using the installation's technology to broadcast their message and to denounce the Prophets as liars.
The team fortified their hold of the gas mine, establishing several Shade turrets on the outside of the mine's various structures, as well as patrolling the premises with Banshees. In defiance to the Covenant, they dressed in armor reminiscent of that traditionally worn by the Sangheili on their homeworld. 343 Guilty Spark reinforced these defenses with the gas mine's Sentinels.
The Hierarchs Truth and Mercy viewed these separatists as a threat to the Covenant and an offense to their religion, thus declaring them "heretics". Against the wishes of the High Council, Truth promoted Thel 'Vadamee, the disgraced former Supreme Commander of the Fleet of Particular Justice to the rank of Arbiter. The Hierarchs then sent 'Vadamee and a Special Operations team led by Special Operations Commander Rtas 'Vadumee to destroy the heretics.
With a heavy storm on Threshold masking their approach, the team silently entered the structure with the element of surprise, encountering only minor resistance from the heretic soldiers. After battling their way to the hangar bay, they discovered that the mine's Sentinels were allied with the heretics. After clearing the landing bay and eliminating the heretic reinforcements, Rtas 'Vadumee sent in a second lance of Covenant troops. With their forces bolstered, the Arbiter and the Special Operations team ventured farther into the facility.
Later, after encountering heavy resistance, the Arbiter was forced to proceed by Banshee. With assistance from a Phantom dropship, 'Vadamee cleared the outside of the facility of enemy soldiers and Banshees. After landing, the Arbiter and another squad of Special Operations Sangheili, including Rtas 'Vadumee, moved inside and pushed toward the center of the facility.
When they entered the structure, the Covenant team encountered numerous Flood forms. After fighting through both the Flood and the gas mine's Sentinels, the Arbiter encountered the leader of the heretics, Sesa 'Refumee. However, 'Refumee escaped by activating a shield door leading to the heart of the facility. 'Vadamee decided to cut the cable that connected the gas mine to a larger installation above, which was designed to be severed in the event of a Flood outbreak; this prompted the rest of the Covenant forces to depart. Eventually, the Arbiter successfully cut the cables, causing the station to fall deeper into Threshold's atmosphere. The Arbiter then chased 'Refumee to his Banshee and followed him to a hangar bay where 'Refumee planned to escape aboard a Seraph fighter. The Arbiter urged 'Refumee to surrender, though the latter refused; the leader of the heretics insisted that the Sangheili were oblivious to the machinations of the Prophets. Unconvinced, the Arbiter demanded he reveal who told him the "lies", prompting 343 Guilty Spark to revealed himself. However, before the monitor could explain the truth of the Halo Array, 'Refumee opened fire on 'Vadamee. 'Refumee deployed two holo-drones and fought 'Vadamee, however the Arbiter eventually emerged victorious.
After 'Refumee's death, 343 Guilty Spark was captured by Tartarus, the Chieftain of the Jiralhanae and was taken before the High Council. Any surviving heretics and Flood forms were certainly killed when the station fell deeper into Threshold's atmosphere. However, it is likely that some heretics survived in a makeshift compound on Threshold's moon, Basis. Other heretics may have remained elsewhere in the galaxy, although without 'Refumee, their influence is probably negligible.
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