Chief, Guilty Spark, the Arbiter, and another Elite aboard High Charity
"Cleanse High Charity. Save Cortana."
Cortana is the 9th campaign mission of Halo 3.
It takes place in High Charity and is presumably involved with the artifact The Key of Osanalan.
Upon completing it on the Normal, Heroic, or Legendary difficulties, the player will earn the "The Key" achievement and 40 Gamerpoints.
References
| Preceded by The Covenant |
Halo 3 Campaign Missions Cortana |
Succeeded by Halo |