Scattered Ember
Survivors of the UNSC frigate Vanguard of Liberty fight to regroup on a Halo ring as the Covenant close in.
The crash
At 0345 ship time, the UNSC frigate Vanguard of Liberty was ambushed by a small Covenant fleet while on patrol. Outgunned and badly damaged, her captain ordered all hands to abandon ship before the frigate made an uncontrolled descent onto the surface of a Halo ring.
The Marines made it to the escape pods, but the pods scattered on launch and were among the last to make planetfall. They landed in unknown terrain, separated from their squadmates, with limited gear and no contact with command, while Covenant ground forces moved in to hunt survivors and secure the crash site. Their mission was to regroup and link up with Colonel Dublin, the ranking surviving officer, who was organizing survivors somewhere on the ring.
Operation Ashfall
With the survivors back under command, Fleet Admiral Lord Hood tasked the Vanguard Marines with keeping Forerunner technology on the ring out of Covenant hands. The Marines pushed to a Forerunner temple, only to find the artifact already gone. Intel pointed them to a nearby Covenant corvette. To reach it they had to knock out the shield generator protecting the ship, which brought a Scarab down on top of them. With the Scarab dead, the Marines boarded the corvette and recovered the artifact from its hold.
Up next: Operation Keystone
ONI analysts, working with Cortana, confirmed the artifact is one fragment of a Forerunner key. The second fragment wasn't aboard. The corvette's navigation logs point to a large Forerunner site, where ONI believes the Covenant have already taken it. Nobody knows what the key opens, and the Marines have to find out before the Covenant do.
Covenant forces are dug in around the site and massing at the temple entrance. Two AA Tyrants have already driven the frigate UNSC Valiant Hearth out of the atmosphere, cutting off artillery and grounding Delta Squad. A shield generator seals the temple itself. The Marines will have to silence the guns, bring down the shield, and get inside to find the second fragment and learn what the Covenant are after.