You were "Master Chief" - in essence a super space marine in great powered armor on the spaceship Pillar of Autumn. A computer program named Cortana was your sidekick, helping you out and providing information to you. Your spaceship came across a gigantic ring, called Halo.

Your enemy was called the Covenant and was made up of goblin type creatures. You headed down to the ring to investigate and see if this was a Covenant craft. There were of course many fights between you and your forces (other lesser armed space marines who nevertheless had great teamwork with you) and the Covenant forces. Each group had their own types of weapons.

You run into yet another computer program, this one called 343 Guilty Spark. Guilty Spark tries to get you to start up Halo, saying it'll help you destroy an even more powerful threat - the Flood. Soon you and the Covenant were both fighting the Flood, which are little, insect critters.

It turned out the way Halo destroys the Flood is to destroy all life forms, period. So you decided to take out Halo itself, hopefully destroying all of the Flood on it. In a death-defying final mission, you manage to get off of Halo just in time, while it blows to tiny bits beneath you. Then you headed home, but unfortunately the ending sequence made it seem like there were more rings - and more flood - still out there.

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