In Halo 2's story mode, the player assumes the roles of the human Master Chief and alien Arbiter in a 26th-century conflict between the United Nations Space Command, the genocidal Covenant, and later, the parasitic Flood.

Aside from variations in storyline, the Arbiter differs from Master Chief only in that his armor lacks a flashlight; instead, it is equipped with a short duration rechargeable form of active camouflage that disappears when the player attacks or takes damage.

Humanity, under the auspices of the United Nations Space Command or UNSC, have developed faster-than-light slipspace travel and colonized numerous worlds.

After the human planet Reach is destroyed, a single ship, The Pillar of Autumn, follows protocol and initiates a random slipspace jump to lead the Covenant away from Earth.

Though the Covenant believe Halo's activation will lead to divine salvation, the humans discover that the rings are actually weapons of last resort, built by the Forerunners to contain a terrifying parasite called the Flood.

Instead of activating the ring, Master Chief and Cortana detonate the Pillar of Autumn's engines, destroying the installation and preventing the escape of the Flood.

For his failure to stop Halo's destruction, the Elite is stripped of his rank, branded a heretic, and tortured by Tartarus, the Chieftain of the Covenant Brutes.

In the ensuing battle, a single ship carrying the Prophet of Regret slips through Earth's defenses and besieges the African city of New Mombasa.

With his fleet destroyed, Regret makes a hasty slipspace jump, and Keyes, Johnson, Cortana, and the Master Chief follow aboard the UNSC ship In Amber Clad.

Regret's death triggers discord among the races of the Covenant, as the Prophets give the Brutes the Elites' traditional role as their honor guard.

Master Chief follows Truth aboard a Forerunner ship leaving the city; Cortana remains behind to destroy High Charity and Halo if Tartarus succeeds in activating the ring.

The Arbiter and Johnson kill Tartarus while Keyes removes the Index; the unexpected deactivation sets Halo and all the other rings on standby for remote activation from a place 343 Guilty Spark calls "the Ark."

[16] Xbox general manager J Allard confirmed Halo 2 was in production at Electronic Entertainment Expo 2002, with a planned release in time for Holiday 2003.

[18] The added publisher support for a sequel allowed greater leeway and the ability to return to more ambitious ideas lost during Combat Evolved's development.

Bungie cofounder and project lead Jason Jones, who had been exhausted shipping Combat Evolved, similarly burned out during Halo 2's production.

"[15][16] Initially, Combat Evolved's multiplayer was supposed to involve larger maps and player counts than what shipped, and members of the team wanted to resurrect those plans for Halo 2.

[18] Bungie promised in previews that the core of this multiplayer would be squad-based online battles between human Spartans and Covenant Elites, with players able to call in airstrikes.

According to Staten, among the elements that did not make it to the finished game was a "horrible scene of betrayal" where Miranda Keyes straps a bomb to the Master Chief's back and throws him into a hole in revenge for her father's death; "Jason was going through a rather difficult breakup at the time and I think that had something to do with it," he said.

[18] Elements like vehicle hijacking were entirely scripted, and in order to keep performance at an acceptable level, a Bungie staff member deleted objects from the game as the player passed through.

The restructuring of the engine meant that there was no playable build of Halo 2 for nearly a year, and assets and environments produced by art and design teams could not be prototyped, bottlenecking development.

Going from having no internet multiplayer to developing a completely new online model was a big challenge to tackle all at once, and as a result we had to leave a lot of things undone in order to meet the ship date commitment that we made to our fans.

"[30] O'Donnell made sure that no part of the game would be completely silent, noting "Ambient sound is one of the main ways to immerse people psychologically.

[43] Launch events were held worldwide, with players waiting for hours in a line that stretched two blocks in Times Square, New York City.

[45] In addition to more traditional forms of promotion, Halo 2 was also part of an elaborate Alternate Reality Game project titled I Love Bees.

[87] Rather than rely solely on user reports of misbehavior, Bungie leveraged its game statistics collection to proactively find cheating players, creating an automated banning system.

The disc contains the game's software update, nine new multiplayer maps, a making-of documentary, and a bonus cinematic called "Another Day on the Beach", among other features.

[95][96] The May 22, 2007, release date was pushed to May 31 after the discovery of partial nudity in the game's map editor—a photograph of Charlie Gough, one of the Lead Engineers, mooning Steve Ballmer during his visit to the studio, was presented as part of the ".ass" error message.

[100] Halo 2 Vista was ported by a small team at Microsoft Game Studios (codenamed Hired Gun) who worked closely with Bungie.

The CBC's Greg Bolton remarked that prior to Halo 2's splashy release, "the video-game industry hadn’t yet found a recognizable public face, a universally acclaimed megastar.

[15][105][106][107] G4's Sterling McGarvey wrote that "Bungie's sequel was a shot in the arm for Xbox Live subscriptions and previewed many of the features that would set the standard for Microsoft's online service on the next machine".