Halo: FIRST STRIKE

The narrative then moves to the debris field of installation 04, right after the events of halo combat envolved. Aboard the longsword cortana and the Master Chief used to escape the destruction, Cortana and the Chief converse, with the Chief insisting that Cortana repeat her scans of the debris for any signs of life.
A battle group of seven covenant Starships enters the system, along with a covenant flagship. Cortana finds three cryopods that were jettisoned from the pillar of autumn prior to its crash on Halo. While she moves the Longsword towards the cryopods, she finds a pelican that landed on a nearby asteroid. As the Chief retrieves the cryopods and returns to the longsword, the pelican takes off and attacks the lead Covenant Starship, diverting attention away from the Longsword. The two small ships link up, and several survivors jump out of the Pelican, namely sergeant jhonson, ODST corporal locklear, warrant officer Shaila P and an ONI liultenant haverson. The Master Chief, having seen a video of Johnson getting infected, slams him into the bulkhead and aims Johnson's pistol squarely at johnson's head, waiting for an explanation on how he could have survived. Johnson through his own words says that they "passed him up because he didn't taste too good". After confirming with Cortana that he isn't infected he releases Johnson.
Together the group manages to board the flagship, called ascendant justice. They fight their way to the bridge and along the way they plug Cortana into the vessel's computer and she effectively kills most of the combat crew by decompressing most of the decks of the vessel. However, she learns that they're running out of time, as the fleet is a prelude to s covenant dignatary's arrival at Halo. The group makes it to the bridge only to confront a Spec Ops Elite wielding an energy sword, whom the Master Chief defeats with the help of johnson and locklear, sustaining a slight injury. The defeat of the Elite warrior allows the humans to gain complete control of the Covenant flagship. In the confusion between the other vessels, the Ascendant Justice enters slipspace, escaping Halo's remains. The group argues about where to go next, but ultimately the Chief persuades them all to return to Reach; first, because the cole protocol forbids them from taking a Covenant vessel to Earth directly; second, because the Chief secretly wants to see what became of his fellow spartans. Haverson sends Johnson, Locklear, and Polaski to the Pelican to get the gear left there. When they are at the Pelican, Johnson contacts the Chief informing him that there is a Spartan in one of the cryotubes.
Meanwhile, back at Earth, UNSC High Command Facility Bravo-6 in Sydney, lieutenant wagner briefs the unsc security council on the destruction of Reach and concludes that they cannot try to retake the planet and must prepare for the final defense of Earth. All Spartans and vessels are assumed destroyed, though they do know that the pillar of autumn escaped destruction. Also revealed here is that colonel james ackerson, who was supposedly reassigned after the events of the fall of reach due to the actions of Cortana, has escaped reassignment and is serving on the Security Council. Ackerson appears almost gleeful that Reach has fallen, but crosses a line when he denounces the Spartans as "freaks", earning a firm rebuke from admiral hood. general strauss considers sending a recon unit to check for survivors, but Ackerson insists that any such mission would not only be suicidal, but pointless, as the Covenant would have left none.

The narrative then returns to Reach where Kelly and Fred, after destroying the Covenant camp, are flying their captured Banshees towards the fallback position at Castle Base. The Covenant fleet in orbit ceases their orbital plasma bombardment, which confuses Fred because it goes against the normal Covenant bombardment doctrine, which has Covenant vessels glass a captured world with continuous criss-crossing plasma fire. After suffering malfunctions in their Banshees, both Spartans crash-land into a pair of Hunters, killing one and disabling the other's fuel-rod cannon. Kelly and Fred happen upon the main Covenant ground camp, which is working to uncover Menachite Mountain and Castle Base. This further worries Fred, causing him to wonder why the Covenant would expend so much manpower to attack Delta Team, but then realizes that they are after something more. Fred and Kelly then steal a pair of Wraith tanks, and blast their way into Castle Base, destroying the digging equipment and much of the Covenant ground armor. There they meet up with the surviving Spartans of Delta Team, including isaac-039, vinh-030 and will-043, all injured. They meet up with Doctor Halsey, who had remained behind to be the fail-safe option to destroy Castle Base should the Covenant get inside. She treats their injuries, and sends them to retrieve some new weapons and MJOLNIR armor replacement upgrades from a secure locker, including the battle rifle and the magnum sidearm.
At the lab, Dr. Halsey discovers an anomaly in Kelly's medical records, which leads her to find Colonel Ackerson's personal AI, araquiel, who was stealing information from Halsey's SPARTAN-II program files. She destroys it using a bypass code she herself had programmed, and gains access to Colonel Ackerson's personal black-ops files, which includes extenisve profles on all her SPARTAN-II's. These were part of a larger file marked "S-III" and hinted towards another secret Spartan program run by Ackerson, which is later explored in halo ghost of onix. In an another file labeled king under the mountain, Halsey discovered that the old titanium mines under Castle may contain an ancient Forerunner artifact, one that the Covenant were currently searching for. The Covenant then invaded the base, and the Spartans and Doctor Halsey escape to the old titanium mines beneath Castle Base, right before its destruction, which blocks their only exit. Having no other alternatives, the Spartans and Dr Halsey venture deep into the tunnels.
In the tunnels, the Spartans receive armor upgrades and Fred discovers several symbols which, upon fred touching one with his bare, bleeding finger, ultimately opens a huge tunnel that leads into an even larger room. In the center of the room, they find a crystal. The Spartans and Halsey find that if they walk straight towards it, it will bend the space around them and, if brought to slipspace, would allow them to travel further using the same amount of energy used in the same vessel. They retrieve the crystal, but the Covenant finds them due to emission of radiation from the crystal. The Covenant land forces inside the giant room using reversed gravity lifts, forcing the humans to retreat. Fred orders Isaac and Vinh to stay behind to form a rearguard action, but they were overwhelmed and presumed killed. The remaining Spartans and Dr. Halsey continue to flee through the tunnels, but as the Covenant follow them, they run into a dead end.

Meanwhile, in Slipspace, john-117 is assisting Seargant Johnson and Polaski in stipping the Pelican of useful gear. It is revealed that the Spartan in the cryo tube is linda-058, who was mortally wounded during the mission on Gamma Station. Although she is declared clinically dead, the Master Chief rushed her to a cryo-pod in the hopes that she could be revived. During the ride in Slipspace, Polaski had perfected piloting a Covenant dropship in ascendant justice's empty hanger bay. As they enter epsilon eridandi, they see what has happened to Reach after the Covenant glassed the planet. They move the flagship closer as they notice that, during the glassing of Reach the Covenant "missed" a spot. The small fleet - consisting of a dozen cruisers, two assault carriers, and three squadrons of seraphs - ask why a flagship is at Reach. While on the ship, the survivors hear a UNSC E-band transmission the E-band transmission is 6 notes Oly Oly Oxen Free. No one on the bridge recognizes it - except the Master Chief. The story flashes back returns to July 14, 2523 as a memory reviews a training mission when the Spartans played capture the flag against tango company. The teenage Spartans win the "game" - despite Tango Company's usage of live-fire rounds - and capture the flag. While hiding from Tango Company Marines searching for the flag, the Spartans make their way to their extraction point. When a Pelican controlled by Tango Company Marines, John shows himself to draw their attention and lures them into a trap set by the other Spartans. John then uses the "Oly Oly Oxen Free" signal to tell his teammates that all is clear.
Back on Ascendant Justice, the human crew debate whether they should go down to Reach in the reinforced Covenant dropship. Cortana looks around to see a spot which can be an extraction site to pick up the people going down to reach. On the way down, cruisers start to surround them in their dropship, but ultimately let them pass. While Cortana continues to explore the flagship's systems, the Covenant AI aboard the ship manages to temporarily gain control of the coms and alerts the Covenant Fleet to the ship's hijacking. Although Cortana is able to destroy the AI, her cover is blown, and she destroys a few of the enemy cruisers before she flees into slipspace. The humans find a canyon with some movement in it. The Chief wanders out alone to see if there is a trap. Haverson backs him up. At the bottom of the ramp Chief senses a single signal. There was no friend-or-foe tag indicating who it belonged to, so the Chief proceeded with caution. The Chief draws his pistol only to lower it discovering that it is anton-044 who had disabled his FoF tag so the Covenant wouldn't discover his location.  He leads the Master Chief to the entrance of a cavern, where two Spartans, grace-093 and li-008 were, both operating chainguns that were bolted to the sides of two boulders. Master Chief and Anton, followed by Grace, enters the cavern. Inside, Admiral Whitcomb was standing at foldout card table, which was the headquarters for Camp Independence.
Admiral Whitcomb asks why the Chief was there, instead of the mission with Captain Keyes deep in Covenant territory. The Chief told him about the events that happened on Halo, and while he was telling the story, Haverson and the others from the dropship arrived. Haverson asks Whitcomb how he is alive, and the Admiral tells Haverson that while everyone was evacuating, he stayed behind because the UNSC was working on a new bomb called the nova-bomb, which possesses enough explosive force to destroy a planet. Whitcomb armed the NOVAs with failsafe tampering detonators and a countdown timer. Whitcomb had a team of Marines, Charlie Company, to help arm the NOVAs, but they were wiped out, but he then saw Red Team on coded COM and "asked" to borrow a few Spartans, who armed the NOVAs and since had given the Covenant trouble with hit-and-run exercises.
The rest of the Red Team is still trapped underground in the tunnels beneath the mountain in the CASTLE facility. The Chief's group uses the Covenant dropship to rescue the remaining Red Team. They enter a huge cavern filled with Covenant forces - a few Elites, Jackals, and mostly Grunts that are clearing a cave-in. They land the dropship a half a kilometer away from the Covenant forces. They manage to destroy the Covenant forces and three Spartans, Kelly, Fred, and Will, emerged from cover. Whitcomb asks if that was everyone and Fred replies that there was one more. That person turns out to be Dr. Halsey who was holding the fist-sized crystal. They are about to leave when they detected Covenant forces and are surrounded by thousands of Covenant forces on each of the twelve levels of the gallery, and crowding the balconies were Grunts, Jackals, Elites and several pairs of Hunters. They all prepare to open fire on them, when a Hunter pair roar with rage and fire their weapons at the Master Chief and his team; the rest of the Covenant forces open fire a split second later.
Back in space, the ascendant justice emerges from Slipspace into a frozen Oort cloud to hide from the Covenant forces because they know that the Ascendant Justice wasn't one of theirs. Cortana eavesdrops on the data streams of the Covenant, using the dissected Covenant AI to help. Cortana discovers through decoding the Coventant transmissions that the location of Earth was now known to the Covenant, and they were preparing a massive attack.

As it turns out, the Covenant forces weren't shooting at the group, but rather the Hunters as they were under orders to take the crystal intact. However, Kelly is incapacitated from taking two direct hits from the Hunters' plasma shots. The Covenant then advance toward the group. Whitcomb signals for Polaski to pick them up and they get whisked out in the nick of time. However, while going up the grav lift, the Covenant begin to use it to push them back down. When Li-008 opens the door to fire Jackhammer rockets up the shaft, Dr. Halsey's crystal changes shape and completely disables the Grav Lift. Once they exit the tunnel, the crystal returns to normal.
In the Ascendant Justice, Cortana uses Engineers to combine the Covenant ship with another ship - the unsc gettisburg, needing two reactors for her maneuver. She jumps into Slipspace, and jumps out right in the middle of the Covenant fleet, at the rendezvous point. The Chief's men get into the Gettysburg-Ascendant Justice (G.A.J.). However, when Cortana jumps back into Slipspace, they don't go into normal Slipspace, and they drag the Covenant fleet with them. The fleet opens fire, but the plasma behaves erratically - doing loops, curving, teleporting, etc. During the fight, Elites that had survived the purge of the Ascendant Justice blow a small hole in its hull. The Spartans and Polaski go out to repair it, but run into the Elites. They fight, but Polaski, Li, and Anton are killed and Kelly is severely wounded. Desperate to escape, Cortana attempts to jump back into normal space. She succeeds, leaving the Covenant stranded in Slipspace, destroyed by sudden decompression of the extended slipspace field created by the crystal.

In the G.A.J.,The Master Chief wakes up after being unconscious since the Slipspace battle. Cortana updated him on the current situation, which includes informing him of the Covenant discovering Earth's location. After disscusing tactical options with both Admiral Whitcomb and Haverson, the Master Chief goes to speak with Dr. Halsey. She talks to him about Johnson and his survival against the Flood. She reveals that Johnson has boren syndrome, which affects the subjects nervous system, making it incompatible with the Flood, and therefore the only known defense against the Flood. Dr. Halsey gives John two data crystals containing information about the Flood, the first one is about Dr. Halsey's analysis and possible inoculation, and the second containing the source file of her conclusion, which would doom Sergeant Johnson as ONI would dissect him to attempt to replicate his condition. She tells him to decide whether he wants to give to Haverson. When the Chief asks why she wants him to make this choice, Dr Halsey says that she is trying to teach him one last lesson, in which to save every person he can, no matter the cost. After he leaves, Halsey and Cortana discuss the crystal and find that it can warp space, gravity, and even time. When her group had found the crystal, the Chief and his group were transported back in time.
For repairs, the group head to the Eridanus Secundus asteroid belt, home of a rebel resistance. As they exit Slipspace, Dr. Halsey announces that Linda will survive and make a full recovery. During not-too-friendly negotiations with Governor Jacob Jiles, a Covenant ship drops out of Slipspace and finds them because of the radiation the crystal emits upon exiting from Slipspace. Despite malfunctioning plasma turrets, the crew of the G.A.J. decide to engage it. When Cortana informs them that the magnetic coils used to shape the plasma aren't working, the Chief comes up with the idea to use the magnetic coils of the Gettysburg's MAC gun to shape it. The ploy works, creating a super-charged plasma torpedo that obliterates the Covenant ship, but also further damages the G.A.J, destroying the super-charged plasma turret. Governor Jiles now agrees to help repair G.A.J before the imminent arrival of more Covenant ships. During the repairs, the remaining Spartans, Johnson, and Locklear disscuss an attempt to stall the Covenant's impending attack on Earth. Johnson points out that the mobile command-and-control battle station, the unyeilding hierophant could be destroyed and possibly stall the Covenant assault. At this time, Halsey sedates Kelly and takes her away to the location she had recorded from Ackerson's logs on Reach. Before she leaves she gives Locklear the crystal and orders him to do whatever is necessary to ensure the Covenant do not retrieve the crystal. After Dr. Halsey leaves, a Covenant fleet arrives and both the survivoirs and the rebels are outnumbered. Repairs are sufficient enough for the G.A.J. to flee into Slipspace. Locklear, devastated by the loss of Polaski, takes the crystal down to a small bay and sets it up with C-7. He blows the crystal up, preventing the Covenant from tracking it through Slipspace, but inadvertantly killing himself in the process.

While the crew of the G.A.J. are able to retrieve a few shards of the crystal, they have more important things on mind: the covenant invasion of earth. cortana reveals that they are gathering at a battle station called the unyeilding hierophant. The chief comes up with a daring plan to blow up the station and put a sizable dent in the fleet: he and the spartans will go to the station in a modified dropship, infiltrate the station, and blow up the reactors, with help from a copy of cortana's subroutines.
The Spartans make it to the station without incident, but are forced to take a detour through a temple complex. There, they encounter brutes for the first time. The chief grapples with a brute, and barely makes it out alive. grace is killed by brute shoots. After the fight with the Brutes, the Chief activates Graces suit's failsafe system, killing many Covenant in the process. They still manage to make it to the reactors, which they successfully rig to explode. The Spartans only have ten minutes to escape, so they commandeer three banshees with the help of Linda's sniper fire. The Master Chief then rescues Linda from oncoming Covenant reinforcements. With the rest of the remaining Spartans, they exit the station and head towards the backside of an unknown moon, but only see the Gettysburg when they made it back to the G.A.J.. The crew had taken the Ascendant Justice's Slipspace engine and installed it on the Gettysburg, while Whitcomb and Haverson have taken the covenant ship. They broadcast a message to the Covenant fleet that if they want the crystal (which they fake with a hologram, as the crystal was destroyed earlier by Locklear) all they have to do is come and get them from the Ascendant Justice - which Admiral Whitcomb and Lieutenant Haverson crash into the central section of the unyeilding hierophant. When the unyeilding hierophant explodes due to the reactor exploding, it destroys the Ascendant Justice along with some five hundred ships of the Covenant invasion force leaving about a dozen ships to attack Earth. The five human survivors of the operation, John-117, Frederic-104, Linda-058, William-043, Sergeant Avery J. Johnson, and cortana proceeded to a random location under Cole Protocol and then return to earth to warn them about the impending Covenant invasion.

In the epilogue, on hight charity, tartarus gives an orb containing shards of the Forerunner crystal to the hight prophet of truth. The Prophet gives Tartarus orders to reward the survivors, then execute them quietly, and punish the incompetent one who lost the Ascendant Justice; "make sure his fate matches the magnitude of his failure .