"Light the Ring. Destroy the Flood."
Halo is the tenth and final Campaign mission of Halo 3. In this level, John-117, Thel 'Vadam and Sergeant Johnson make their way towards the Control Room in order to activate the ring using the Index from the first Halo encountered.
However, the Gravemind sends Flood Combat Forms (and later Pure Forms), carried by Flood dispersal pods, to try to stop them. This level is also the second mission in the Halo series to bear the name of another mission, following the second mission of the first game.
Upon completing it on Normal or higher, the player unlocks the Return achievement. If the player gets 15,000 points or more in the meta game, they will unlock the Reclaimer achievement.
Finishing this level will lead into the final credits and cutscenes, finishing the level on Legendary will lead to the scene where Halo 4 starts.