The Covenant (level)

The Covenant is the tentative title of the 8th campaign mission of Halo 3.

It takes place in The Ark. As the purpose of the level is to "stop Truth", it is possible that the ultimate objective of the level is to kill the Prophet of Truth in a boss-battle of sorts.

Upon completing it on the Normal, Heroic, or Legendary difficulties, the player will earn the "Last Stand" achievement and 40 Gamerpoints.

http://halo.wikia.com/wiki/Image:Arbitertruth.jpg This is the cutscene after defeating Truth.