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Having escaped the destruction of the UNSC Pillar of Autumn, Fireteam Raven find themselves stranded on a mysterious ringworld. The group are guided to regroup with other UNSC forces via a mobile link with Wellsley, expected to take 28 hours. The mission begins with Fireteam Raven linking up with Lieutenant Melissa McKay to assist in the raid on the downed Autumn. The raid is successful and Raven assists UNSC forces in retrieving supplies and equipment from the ship.
A Warthog pulls up next to Fireteam Raven. Ramos enters the side seat and Hudson enters the gun, while Lang and Graves sit on either side of the gun. The Warthog joins the convoy as the camera switches to first person view. The players are operating the M41 Vulcan chainguns on the back of the vehicle. In the distance, the wreckage of the Pillar of Autumn can be seen, with Threshold behind it.
The convoy begins firing upon the attacking Type-26 Banshees, while several Type-25 Spirits can be seen overhead. Several dozen Banshees are destroyed by the Warthog's chainguns, before a wing of three Falcons and three Pelicans crest the horizon, with the Pelicans dropping off additional Warthogs to join the battle. The convoy is then attacked by a wave of Ghosts, with the Warthog stopping to let the players fire on the attacking forces. The squad is reinforced by a small fleet of Warthogs who help mop up the last Ghosts, though one is soon destroyed by a plasma mortar fired by a Type-26 Wraith.
The Warthog then engages two Wraiths, followed by another pair reinforced by more Banshees. By this time, the convoy has reached the downed vessel, and is now attacked by several more squadrons of Banshee. The squad finds themselves face-to-face with a Scorpion tank.
As Wellsley speaks, a combined force of Marines, tanks and Warthogs form a line of defense, combining their fire to hold off the assault of a Wraith, a Ghost and some infantry. Raven's Warthog takes them past this line, in time to see a Mongoose blown up. The Warthog itself is then hit by a mortar, and Raven ejected from the vehicle. The squad then equip their MA5B assault rifles and begin engaging a Spirit dropship, firing upon its infantry complement as they exit the troop bay of the vehicle. The squad begins to retreat as a Wraith pushes them back, though a shell from a Scorpion kills the Covenant vehicle, its momentum pushing it forward. The squad then turn around to see several Kig-Yar advancing down the hill behind the UNSC line, supported by a swarm of Yanme'e. The creatures swarm the convoy, picking up UNSC marines mounting the M41 cannons on the Warthogs and dropping them from high in the air. A Sangheili Major armed with an energy sword emerges from behind a Warthog and impales one of the surviving Marines, as the squad hold off more and more Covenant infantry.
Fireteam Raven then pick up and equip M41 SPNKR rocket launchers found on the corpse of a dead marine, utilizing the weapons to hold off air attacks by Banshee fighters once more, before destroying a Spirit dropship with the weapons. Which crashes to the ground in the midst of a Covenant charge. As Fireteam Raven once again turns around, the sum total of the UNSC defense can be seen, with many Scorpions and Warthogs joining the defense. In the distance, Covenant infantry can be seen retreating from the site, as they are fired upon from afar. The camera then swtiches to show Fireteam Raven, with Graves holding a portable hologram of Wellsley.
The camera then pans to show the UNSC convoy beginning to retreat from the Autumn back to their base and the mission ends.