Fireteam Crimson is sent to investigate the last known location of Fireteam Switchback, after receiving a transmition sent to Infinity talking about a Covenant harvester in the area. After being dropped off by Murphy in a hijacked phantom, Crimson comes into contact with many prometheans. The team loacates Switchbacks IFF tags, but with no sign of the spartans. The tags are also empty, leaving no sign of Switchback, or what happened to them. Putting aside the mystery of Switchback, the team on Infinity instruct Crimson team to shutdown the Harvester for good. They get the covenant's attention by destroying some equipment, and enter the Harvester. Crimson destroys some key components of the harvester, and head to the LZ for pickup, again facing many prometheans. Once the zone is clear, Murphy returns to take Crimson home to Infinity.
If you look on the floor near the control panel in the center of the top deck of the Harvester, you can see Lekgolo worms crawling in the pipes.
The Lekgolo worms are also strange, as they are seen crawling in the pipes, not making up the insides (like a scarab). This would sugest that the Harvester was found by the covenent, and then Lekolo worms were used to assume control.