Battle of Aktis IV
Determined to combine the halves of the Janus Key and take them to the Absolute Record to fulfill the Librarian's plan, Dr. Catherine Halsey concocted a plan to recover the other half of the key from the UNSC without having to board the UNSC Infinity. Following the Battle of Oban Infinity made a slipspace jump towards Galileo II base so that Dr. Henry Glassman could further study their half of the key. However, the Infinity suddenly reappeared in an asteroid belt, colliding with an asteroid and causing some damage inside the ship. The Infinity jumped to slipspace again, just to reappear a quarter of a kilometer of her last position. Unbeknownst to the crew of Infinity, they were being stranded in the system by a Forerunner artifact, recovered by 'Mdama before Requiem exploded. The artifact allowed Halsey to contact the Infinity's Forerunner components, including her slipspace drive, and stuck them in the system. The failed attack on Oban was actually a bold move to attract the Infinity near the artifact and be able to connect the artifact and Infinity's drive. After checking the Infinity's engine room, Roland found an unusual energy reading coming from the equator of an uncharted planet near their position. Glassman and Captain Thomas Lasky supposed that the location was the source of the problem and Sarah Palmer prepared to send a team to the planet.
Lasky deployed a reconnaissance team to investigate a potential source of interference emanating from the surface of the planet, provisionally designated Aktis IV. The mysterious signal originated from an island in a large ocean of an opaque, foamy substance impenetrable to Infinity's sensors. Upon landing, Spartan Fireteam Majestic and Commander Palmer engaged and defeated a detachment of Covenant forces and subsequently discovered a recently-excavated Forerunner structure. Afterwards Dr. Glassman arrived and examined the Forerunner structure, with the Spartans providing cover. Glassman theorized the structure to be part of a translocation grid and soon discovered a Forerunner artifact with indentations in the shape of the halves of the Janus Key, seemingly suggesting this was where the Key was meant to be placed. However, Halsey and 'Mdama were monitoring the events and the artifact was in fact a decoy created to deceive the UNSC into taking their half of the Janus Key to the surface. Halsey believed that the UNSC would never suspect a trap as no one but Glassman would realize the Key's true value.
On the planet, Glassman requested to have lab equipment brought to the Forerunner site along with the UNSC's half of the Janus Key in order to analyze the artifact; Palmer reluctantly agreed and contacted Lasky. Although 'Mdama had troops standing at the ready, waiting for the signal to ambush the UNSC forces and take the Key, Halsey reminded Jul to exercise extreme care to avoid damaging the Key until it was safely in their possession. While the Janus Key was being prepared for transport, Roland questioned the decision to move the artifact to the surface as it may distract Glassman from his task of ascertain the origin of the interference keeping Infinity stranded. However, Lasky was confident Palmer would be able to keep Glassman focused and believed taking the Key to the surface would not cost them anything either way.
Split among the Covenant remnants
As the Pelican carrying the Key approached the Forerunner site accompanied by a Broadsword escort, Commander Palmer charged Gabriel Thorne with moving the materials to the Forerunner structure. However, the incoming UNSC craft were suddenly struck by Covenant anti-air artillery operated by forces under the command of Sali 'Nyon, a Sangheili rebel who sought to overthrow Jul 'Mdama. Mdama and Halsey were caught off guard by this turn of events as 'Mdama had given no order to fire, nor did he have forces deployed in the area. Meanwhile, the shipmaster of Breath of Annihilation, one of 'Mdama's CAS-class assault carriers, received word on the unauthorized attack. Assuming he would be blamed for the incident since the unit responsible would likely be one under his direct command, the shipmaster chose not to wait for 'Mdama's signal and ordered his fleet to proceed with their planned attack against the UNSC forces. The Breath of Annihilation and the rest of 'Mdama's fleet then emerged from the foam ocean, having remained concealed underneath. As 'Mdama's Covenant began their onslaught, the Spartans on the island were quickly forced to pull back into the Forerunner structure while Infinity prepared to deploy reinforcements.
On the Song of Retribution, Halsey and 'Mdama argued about their next course of action. Halsey urged 'Mdama to reposition his fleet to draw the UNSC's attention away from the Pelican's crash site, but Jul was confident they would be able to take the Janus Key via a full-on assault despite the unexpected complication. Halsey then requested 'Mdama to scour the Pelican's crash site herself, but Jul had her remain on the ship while he intended to personally land on the surface, acquire the artifact, and punish those responsible for compromising the plan. On Aktis IV, Sali 'Nyon and several of his followers searched the Pelican's crash site. After discovering the half of the Janus Key, 'Nyon proclaimed his goal to expose 'Mdama as a fraud and assume leadership of the new Covenant, declaring himself "the one true prophet".
Having revealed itself from the foam ocean, Jul 'Mdama's fleet surrounded Infinity and blocked the UNSC flagship off in low orbit over Aktis IV for over seven hours. Commander Palmer, Fireteam Majestic and Glassman remained under attack by Covenant forces inside the Forerunner structure and were unable to establish contact with Infinity. While they retreated inside the facility, Spartan Carlo Hoya was left behind outside. Palmer ordered Glassman to get the structure's teleportation grid online before Jul 'Mdama's Covenant breached their defenses. Glassman informed her that the grid was online but he needed to decode the coordinates to the exit portal and there was no chance to successfully escape to a safer location.
Within Jul 'Mdama's Covenant fleet, Sali 'Nyon broadcast a transmission to incite Jul's forces to join him in his rebellion against 'Mdama. Meanwhile, Jul 'Mdama and his forces continued to personally track down and eliminate Sali 'Nyon's followers on the planet. A Sangheili Zealot advised him to return to the Song of Retribution for his safety, but 'Mdama declined. When informed that his forces were about to breach the structure where the UNSC forces remained barricaded, 'Mdama ordered his forces to kill all the humans when they entered the site, except Glassman as he had a special punishment for him. Jul entered a Phantom where he was contacted by Dr. Halsey, who stressed the importance of recovering the Janus Key over 'Nyon's rebellion. Because of the ongoing crisis, 'Mdama fulfilled Halsey's request to personally land on the planet to acquire the Janus Key. Halsey subsequently departed for the planet aboard a Phantom, escorted by Jul's forces.
In the jungle Hoya was facing what were, unknown to him, 'Nyon's forces. A Zealot was about to kill him when a Promethean Knight loyal to 'Mdama kicked the Zealot, inadvertently saving Hoya in the process. Hoya fell off a cliff and spotted Dr. Halsey aboard a Phantom. Meanwhile, 'Mdama's Covenant breached the Forerunner structure where the Spartans had taken shelter and attacked them. Ray informed Palmer that Hoya had spotted Dr. Halsey.
In Sali 'Nyon's hideout on the planet, some of his followers began to question the feasibility of his rebellion. 'Nyon continued to reassure his followers that the Forerunners had blessed them, citing his acquisition of the half of the Janus Key as proof. However, one Sangheili Minor, believing that the Promethean constructs' allegiance to Jul 'Mdama was evidence to the contrary, decided to leave 'Nyon's rebel faction and stole the Janus Key half in 'Nyon's position, intending to offer it to 'Mdama as a gesture of penance.
Inside the Forerunner structure, Glassman opened the teleportation grid. At Palmer's request, Glassman opened portals to both the jungle and the other end of the island. She ordered Tedra Grant, Glassman and three other Spartans to take the latter portal while Palmer, Ray and Thorne took the former. On the other end of the island, Infinity had managed to deploy two Mantises as reinforcements. As they were fighting Jul 'Mdama's Covenant forces, Grant's team arrived through the portal and were almost killed by friendly fire from the Mantises.
Upon traveling through the portal, Palmer, Ray and Thorne scouted the jungle when they spotted the Sangheili Minor who had defected from 'Nyon's forces in a Ghost. The Minor contacted a Zealot of Jul's Covenant and told him he wanted to rejoin 'Mdama, having reached the conclusion that Jul was the true Didact's Hand because the Prometheans would never obey an impostor. He then revealed he had the half of the Janus Key stolen by 'Nyon, and he would lead them to 'Nyon's hideout. The Zealot ordered him to conceal himself until they arrived and established a rendezvous point. Thorne and Ray intended to ambush the Minor in order to take the Janus Key before Dr. Halsey arrived with a greater force. However, Palmer instead ordered them to hold off and wait until Halsey arrived so they could catch the doctor by surprise.
After waiting for an opportune moment to ambush Dr. Halsey, Commander Palmer and Spartans Thorne and Ray observed a group of Jul 'Mdama's Phantoms arrive to claim the Janus Key half from the Sangheili defector. Elsewhere on Aktis IV, Jul 'Mdama continued to eliminate 'Nyon's followers. Jul was informed that his forces had excavators in position and were ready to be used against 'Nyon's rebels. With the rebellion in its death throes, Jul was confident that Halsey and her escort would not be ambushed and diverted most of the Phantoms to deal with the UNSC forces elsewhere on the island. While Infinity and its sub-vessels continued to engage 'Mdama's fleet, Lasky queried Roland about Palmer's whereabouts. The AI informed him that he could only contact Spartan Grant's team, while Palmer had gone off on a mission of her own and taken two of the Spartans with her.
Dr. Halsey and her Zealot escort met with the Sangheili defector. The Minor was forced to turn over the artifact and was then promptly executed by one of the Zealots as he had outlived his usefulness; 'Mdama's faction already knew the location of Sali 'Nyon's hideout. Before they could return to the Song of Retribution, the group was ambushed by Palmer, Thorne and Ray. With their Phantom surrounded by the Spartans, Halsey and a Zealot fled to the forest. Palmer gave chase while leaving Thorne and Ray to deal with 'Mdama's Covenant forces. In the jungle, Palmer killed the Zealot guarding Halsey and captured the doctor.
As Palmer was leading Halsey through the jungle the doctor began to argue with Palmer. Revealing that ONI was using her as a convenient scapegoat, Halsey managed to cloud Palmer's judgment momentarily and ran off. Palmer gave chase, only to come face to face with a Harvester. Halsey got away while the ground below Palmer was blasted by the Harvester's main beam. Palmer fell off a cliff and attempted to propel herself back up using her armor's thrusters, but she was hit in the back of the head by a falling rock and fell into a crevice. Halsey contacted Jul 'Mdama and was picked up by a Phantom.
Three days later, after the UNSC forces had returned to Infinity, Lasky met with Palmer in an interrogation room. Lasky informed her that two ONI agents were demanding to speak with her and that Ray and Thorne were furious about her behavior on the planet. While Roland stalled the ONI agents Lasky asked Palmer to tell him what happened. Palmer explained that she could not bring herself to kill Halsey and that the doctor was able to distract her and get away with the Janus Key, thus giving Jul 'Mdama access to both halves of the artifact. Meanwhile, Jul and Halsey used the combined Janus Key to project a holographic map pinpointing the location of the Absolute Record.
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