
With the help of his fellow Marines and the ship's Artificial Intelligence, Cortana, the Master Chief discovers the secrets of Halo while also fighting off fleets of the Covenant. The main character, Master Chief Petty Officer John-117 is aboard this ship at the time nearing its destruction. The "Halo" in the title refers to an enormous artificial space habitat similar to a Culture Orbital discovered by the warship known as the Pillar of Autumn. Halo, like Bungie's previous releases such as the Marathon series, has an intricate plot. Halo Combat Evolved Campaign consists of 10 levels: The PC version of Halo: Combat Evolved allows only one player to play through the campaign.

The Xbox version of Halo: Combat Evolved allows one player to play the campaign alone, as well as allow two players to play through the campaign in split screen. This method of storyline delivery is common among modern video games. It is presented to the player through an instruction manual, scripted events and conversations during the game, and a number of cut-scenes rendered using the game's graphics engine. There is a single ending in contrast to other first person shooters such as Deus Ex. 1.3.2 The Human Colonization of the Orion Arm.
