Fireteam Crimson is sent to the "Warrens" to help Fireteam Lancer destroy a Covenant nest. Complicating things, a shield wall is blocking off access to the base. Further complicating matters, the three generators powering the shield wall are camouflaged. While Miller tries to find a way to reveal the generators, he picks up the mysterious SOS again. Eventually, he determines that the camouflage around the generators is controlled by a certain Elite. Crimson kills the target Elite. They then destroy the now exposed shield generators, bringing the shield wall down.
Crimson and Lancer move through the canyon and reach the entrance to the Covenant base. Though the front door is locked, the Spartans provoke the Covenant into opening the door. After clearing out all of the Covenant outside the structure, Crimson heads into the caves. Inside, they detect the SOS again. Miller determines the signal is coming from inside the cavern. Crimson proceeds to eliminate all the Covenant inside, as well as any reinforcements that arrive. Miller then informs Palmer that Poker Squad has captured an Elite who is offering to give up the location of a Covenant listening post in exchange for his life. Palmer agrees to the deal and orders Poker Squad to investigate.
Crimson continues making their way through the caverns, eventually arriving at a Forerunner structure. After defeating the Covenant and Prometheans guarding it, Crimson proceeds inside. There they find Fireteam Switchback - who had gone missing while trying to disrupt a Covenant excavation - trapped behind a shield wall. Spartan Gale reports that their leader was killed and that the rest of the team have been sending out the SOS on the Covenant's own communications network. Crimson frees Switchback and leads them out of the caves. The two Fireteams defeat a final wave of Covenant reinforcements at the exit. The Spartans make it back outside where they are picked up by Murphy's Pelican.
Commander Palmer congratulates Crimson on not only completing their mission, but also rescuing Switchback.
Fade in to a ground shot of a Covenant-occupied canyon. Camera pans upward as two Pelicans fly overhead.
Switch to an aerial shot following the Pelicans.
Switch back to the ground. A pair of Unggoy look up as the two Pelicans come in for a landing.
One Pelican drops a Warthog on top of one of the Unggoy, killing him. The other Unggoy starts to flee, but the second Pelican also drops a Warthog, crushing him too.
A Phantom deploys a Wraith.
Marker appears on one of the Elites.
Crimson kills the target Elite.
Crimson destroys all three shield generators. The shield wall goes down.
Crimson moves further into the canyon and soon reaches the entrance to the cave. A massive Forerunner door bars their way.
Crimson proceeds to neutralize the Covenant stationed outside the door. The door begins to open up.
Covenant forces emerge from behind the door. Crimson engages and defeats them.
Crimson heads into the cavern where they find a large array of Forerunner structures built into the caves.
A series of electronic noises are heard over the COM.
Crimson engages multiple Covenant infantry, along with Ghosts and Shade turrets.
Enemy Phantom enters the cavern through an opening and deploys a Wraith.
Another Wraith arrives.
Crimson finally defeats all the Covenant reinforcements.
Crimson reaches a particular Forerunner structure. They eliminate the Covenant guarding it.
Crimson opens the door. Covenant and Promethean forces emerge.
Once most enemies are down:
Crimson finishes off all remaining enemies. They move into the structure where they find a group of Spartans trapped behind a shield wall.
Crimson deactivates the shield wall trapping Switchback.
Switchback grabs some nearby weapons. Crimson leads them toward the exit.
Crimson and Switchback engage a final group of Covenant blocking the exit. The two Spartan fireteams make short work of the enemy troops. At the same time, Murphy’s Pelican engages and destroys a Covenant Phantom.
The Spartans exit the caverns and reach the evac zone. Murphy’s Pelican arrives to pick them up.
Fade to black.