The Search for Halsey
From Halopedia, the Halo wiki
In the wake of Doctor Catherine Halsey's abduction by Jul 'Mdama, all Spartan Fireteams have been reassigned to recover her. Fireteam Crimson is sent to "Cyclone" in hopes of tracing a transmission made by Halsey. They are assisted by Doctor Lani Truman from Infinity Science.
After Crimson takes out the Covenant guarding the area, Truman sends the Spartans to a specific structure containing a Covenant comm terminal. To their surprise, the structure's door opens for them. Crimson takes out the Hunters and Elites inside and accesses the comm terminal. From it, they learn that Jul 'Mdama has ordered all Covenant forces to meet at a place called "Librarian's Rest". Roland, meanwhile, tracks down where Halsey's transmission was sent to next. It's in an area already occupied by Marines.
While Truman attempts to trace the rest of Halsey's transmissions in hopes of determining where "Librarian's Rest" is located, Miller sends Crimson to investigate a sudden power spike at another structure. On the way to investigate, the Spartans come under attack by Promethean forces. Crimson fends off the Prometheans and finds a control console where the energy spike apparently originated from. They are unable to determine its purpose, but Roland notes that the terminal and Halsey's encrypted comm stream are using the same modulation frequency, indicating they are connected somehow.
Just then another wave of Prometheans attacks Crimson's location. Unexpectedly, some friendly beam turrets are activated and assist Crimson in the fight. A group of Sentinels also comes to Crimson's aid. Furthermore, an unidentified presence inside the system assists Truman in decrypting Halsey's transmissions. The decryption stops at 99%, and at the same time the terminal's modulation frequency also stops. On a hunch, Miller orders Crimson to activate the terminal. This generates a massive data stream from a nearby tower, but Truman can't analyze it properly.
Miller orders Crimson to head to the area where Roland has determined Halsey's transmission was relayed to next.
All dialogue is spoken through the COM.
Cut to "Cyclone" on Requiem. Fireteam Crimson’s Pelican approaches.
Crimson’s Pelican lands at "Cyclone."
Crimson engages Covenant forces nearby.
A Covenant Phantom descends and deploys enemy reinforcements.
Once most Covenant troops are killed:
Once all the Covenant are defeated:
Waypoint appears on HUD.
Crimson moves in to investigate the structure. Upon reaching the door Truman directed them to, it dissolves. A Hunter emerges from the structure.
Crimson kills the Hunter and enters the building. More Covenant are waiting inside including a second Hunter.
Crimson clears out the structure.
A terminal is marked. Crimson activates it. They hear a transmission spoken in Sangheili:
Roland translates for them.
Crimson heads off to investigate. As they approach their objective, Prometheans suddenly phase onto the battlefield.
Crimson battle and defeat the Prometheans. They move into an opening in the structure and discover a terminal crackling with energy.
New enemy contacts appear.
Crimson engages the Prometheans once again. Several beam turrets materialize around the structure and begin firing upon the Prometheans.
If one of the allied defense turrets is disabled:
During the middle of the battle:
Once the area is clear:
A new wave of Promethean Watchers and Crawlers attack Crimson. A flock of Aggressor Sentinels unexpectedly come to the Spartans’ aid.
The combined power of Crimson, the Sentinels, and the beam turrets make short work of the Promethean attackers.
Crimson activates the power source. The Sentinels start flying away.
The Sentinels surround a tower and begin zapping it with their beams. The tower unfolds and emits a massive horizontal beam of light through a row of ring-like structures.
Crimson heads to the LZ and is picked up by a Pelican.