Half-Life 2: Episode One (stylized as HλLF-LIFE2: EPISODE ONE) is a first-person shooter video game, the first in an intended series of episodes that would serve as the sequels to Half-Life 2 (2004). It was developed by Valve Corporation and released on June 1, 2006. Initially called Half-Life 2: Aftermath, the game was renamed Episode One after Valve became confident in using an episodic structure for the game. Episode One uses the same game engine, Source, as Half-Life 2. The game debuted new lighting and animation technologies, as well as AI sidekick enhancements.

Half-Life 2: Episode One
Half-Life 2 - Episode One.jpg
Cover art showing key character Alyx Vance
Developer(s)Valve Corporation
Publisher(s)Valve Corporation
Composer(s)Kelly Bailey
Platform(s)Windows, Xbox 360, PlayStation 3, OS X, Linux
Genre(s)First-person shooter

The game's events take place immediately after those in Half-Life 2, in and around war-torn City 17. Episode One follows scientist Gordon Freeman and his companion Alyx Vance in humanity's continuing struggle against the alien civilization known as the Combine. When the story begins, Gordon wakes up outside the enemy's base of operations, the Citadel, after being left unconscious from the concluding events of Half-Life 2. During the course of the game, Gordon travels with Alyx as they attempt to evacuate the city. As the game comes to an end, Gordon and Alyx are caught in a major accident, and their fates are revealed in the sequel, Episode Two.

Valve views episodes One through Three tantamount to a standalone release. Episode One is available as part of a bundle package known as The Orange Box, which also includes Half-Life 2, Episode Two, Team Fortress 2, and Portal. Episode One received a generally positive critical reaction, and the co-operative aspects of the gameplay received particular praise, although the game's short length was criticized.


In Episode One, players make their way through a linear series of levels and encounter various enemies and allies. The gameplay is broken up between combat-oriented challenges and physics-based puzzles.[5] Episode One integrates tutorial-like tasks into the story to familiarize the player with new gameplay mechanics without breaking immersion.[6] A head-up display appears on the screen to display the character's health, energy, and ammunition.[7] Throughout the course of the game, the player accesses new weapons and ammunition that are used to defend the character from enemy forces.[8] Unlike in Half-Life 2, where Gordon's first weapon is the crowbar, Gordon first acquires the Gravity Gun, which plays a crucial role in the game by allowing the player to use physics to manipulate objects at a distance in both combat and puzzle-solving scenarios.[6]

The AI for Alyx Vance, Gordon's companion, was explicitly designed for co-operative play in Episode One to complement the player's abilities. The developers described Alyx's programming for Episode One as a "personality code" as opposed to an "AI code", emphasizing the attention they gave to make Alyx a unique and believable companion. For part of the code, she was explicitly programmed to avoid performing too many mechanical or repetitive actions, such as repeating lines of dialogue or performing certain routines in combat situations.[9] Examples of this co-operative gameplay include combat in underground levels. In this scenario, the player can conserve their ammunition by using a flashlight to help Alyx spot and kill oncoming enemies.[10] Similarly, Alyx will often take up strategic positions and provide covering fire to keep the player safe while they travel to a certain area or perform certain actions.[11]



The original Half-Life takes place at a remote laboratory called the Black Mesa Research Facility. The player takes on the role of Gordon Freeman, a scientist involved in an accident that opens an inter-dimensional portal to the world of Xen and floods the facility with hostile alien creatures. After the player guides him in an attempt to escape the facility and close the portal, the game ends with a mysterious figure who offers Freeman employment. The protagonist is subsequently put into stasis by this mysterious character known as the G-Man.[12]

Half-Life 2 picks up the story, in which the G-Man takes Freeman out of stasis and inserts him on a train en route to City 17 an indeterminate number of years after the events of the first game, with Earth now enslaved by the transhuman forces of the Combine. The player guides Gordon to aid in humanity's struggle against the Combine and its human representative, Dr. Wallace Breen. He oversees the occupation from his base of operations in the Citadel, a monolithic building at the heart of City 17. Fighting alongside Gordon is an underground resistance led by former colleague Dr. Eli Vance, as well other allies including Dr. Vance's daughter Alyx Vance and the enigmatic Vortigaunts, an alien species. Half-Life 2 ends with a climactic battle atop the Citadel that inflicts critical damage to its dark fusion reactor. When it seems as if Alyx and Gordon are to be engulfed by the explosion, the G-Man appears once more. After giving a cryptic speech, he extracts Gordon from danger and places him in stasis once again.[12]


Alyx talks with the resistance leaders outside the Citadel. The new HDR rendering and Phong shading effects are visible.

After the explosion of the Citadel reactor from which Gordon was extracted by the G-Man and where Alyx Vance was left behind, time suddenly freezes. Several Vortigaunts appear and rescue Alyx from the blast. After she is rescued, the Vortigaunts appear before the G-Man and stand between him and Gordon. They teleport Gordon away from the scene, much to the G-Man's displeasure.

D0g retrieves Gordon out from under some rubble outside the Citadel, and Gordon reunites with Alyx, who is relieved to see him. Alyx contacts Eli Vance and Isaac Kleiner, who have escaped the city, and is informed the Citadel's core is at risk of exploding at any moment. Kleiner states the explosion could be large enough to level the whole of City 17, and the only way for them to survive is to re-enter the Citadel and slow the core's progression toward meltdown. Eli reluctantly agrees when he sees no other option.

Alyx and Gordon re-enter the now-decaying Citadel to try to stabilize the core; Gordon is successful in re-engaging the reactor's containment field, which delays the explosion. Alyx discovers the Combine are deliberately accelerating the destruction of the Citadel to send a "transmission packet" to the Combine's homeworld. She downloads a copy of the message, which causes the Combine to prioritize them as targets. Alyx also downloads a transmission from Dr. Judith Mossman, in which she mentions a "project" she has located, before she is cut off by a Combine attack. Afterward, Alyx and Gordon board a train to escape the Citadel.

The train derails en route, forcing the duo to proceed on foot. As they fight through the disorganized Combine forces and rampant alien infestations, Kleiner appears on the screens Breen once used to pass out propaganda, and gives out useful updates to the evacuating citizens about the latest turn of events as well as reiterating the Citadel's imminent collapse. Alyx and Gordon eventually meet up with Barney Calhoun and a group of other survivors who are preparing to move on a train station to escape City 17. Alyx and Gordon provide cover for the passengers as they board.

To keep the survivors safe, Alyx and Gordon opt to take a different train. They manage to escape just as the reactor begins to detonate; the energy sends out the Combine's message. Several pods containing Combine Advisors are ejected from the Citadel as it detonates. The resulting shockwave catches the train, derailing it.


Half-Life 2: Episode One is the first in a trilogy of episodes serving as the sequel of the 2004 first-person shooter video game Half-Life 2.[13] In February 2006, Valve announced that they would be releasing a trilogy of episodes covering the same story arc. While the plots and dialogue of Half-Life and Half-Life 2 were written solely by Valve's in-house writer Marc Laidlaw, the Half-Life 2 Episodes were collaboratively written by Laidlaw, Chet Faliszek, and Erik Wolpaw, with Laidlaw retaining overall leadership of the group.[14]

Valve explained that the focus of Episode One was character development, particularly that of Gordon's companion Alyx, because she accompanies the player for almost the entire game.[15] Project lead Robin Walker discussed the reasoning behind this approach in an article announcing the game in the May 2005 issue of PC Gamer UK, saying, "It's kind of ironic that despite so much of the theme of Half-Life 2 being about other characters and other people, you spent most of the game alone."[16] Laidlaw expanded further on the game's premise, saying,

Episode One deals with the events and issues set in motion during Half-Life 2. You've done critical damage to the Citadel. The whole place is going to go up, taking out City 17 and what's in its immediate radius. You and Alyx are leading the flight from the city getting up close and personal with some of the creatures and sights from the end of the game.[16]

It was later confirmed that players would reprise the role of Gordon Freeman, unlike the original Half-Life expansion packs, which all dealt with different characters. Valve decided to develop Episode One in-house, as opposed to working with outside contractors as with previous expansions, because the company was already comfortable with the technology and construction tools of Half-Life 2.[17]

Because of Alyx's significant involvement in the game, Valve made modifications to her AI that allowed her to react to the player's actions. Changes include commentating on objects the player manipulates or obstacles they have overcome. She also acts as an essential device in both plot exposition and directing the player's journey, often vocalizing what the player is required to do next to progress.[18] The developers explained that a large part of their focus was creating not only a believable companion for the player, but also one that did not obstruct the player's actions. They wanted to allow the player to dictate his/her own pace and method of overcoming any challenges faced without being hindered. This meant that Valve often had to scale back Alyx's input and dialogue during the player's journey so they would not feel pressured to progress and consequently object to her presence.[18] The developers also placed what they described as hero moments throughout the game, which allow the player to single-handedly overcome obstacles such as particularly challenging enemies, during which Alyx takes the role of an observer and gives the player praise and adulation for their heroic feats.[18] Playtesters were used extensively by the developers throughout the entirety of the game's creation so that Valve could continually gauge the effectiveness of in-game scenarios as well as the difficulty.[19]

The game runs on an upgraded version of Valve's proprietary Source engine, and features both the engine's advanced lighting effects, and a new version of its facial animation/expression technology.[19] Upgrades to enemy AI allow Combine soldiers to utilize tactics previously unavailable to them. For example, Combine soldiers were given the ability to crouch while being fired upon so they could duck underneath the player's line of fire.[18] The game's soundtrack was composed by Kelly Bailey.[14] The music is used sparingly throughout; it plays primarily during scenes of major plot developments or particularly important action sequences such as large battles or when encountering a new enemy.[18]

While no new locales were introduced in Episode One, extensive alterations were made to the appearance of both City 17 where the game takes place and the Citadel from the end of Half-Life 2 to reflect the changing shape of the world and remind the player that their actions have major effects on the storyline.[20] The Citadel has degenerated from the cold, alien, and imposing fortress of the previous game into an extremely unstable state. This provides a visual cue to the player of the catastrophic damage they inflicted, and it allows for the introduction of new gameplay elements that accentuate the dangers which come with the Citadel's imminent collapse. It also serves a thematic purpose by highlighting the weakening of the Combine's dominance in City 17. Likewise, City 17 has been altered to reflect the aftermath of the resistance's open rebellion, with vast swathes of destroyed buildings, and the introduction of foes previously kept outside its confines in Half-Life 2 to emphasize the scale of the uprising.[21]

Release and receptionEdit

Aggregate scores
Review scores
Game RevolutionB[5]
GameSpy     [24]
PC Gamer (UK)90%[6]
PC Gamer (US)85%[25]

Upon release, Episode One was sold in both retail stores[28] and Valve's online Steam distribution system, where it was sold at a discount price.[29] The game was also distributed by Electronic Arts as both a standalone release and as part of Half-Life 2: Platinum Collection.[30] It was available for pre-load and pre-purchase through Steam on May 1, 2006, with Half-Life Deathmatch: Source and Half-Life 2: Deathmatch immediately available for play as part of the package.[31] Episode One is available as part of a bundle package known as The Orange Box, which also includes Half-Life 2, Episode Two, Team Fortress 2, and Portal; and is available for Mac, PC, Xbox 360, and PlayStation 3.[32][33] About 1.4 million retail copies of Episode One were sold by 2008.[34]

Response to Episode One was generally positive, and reviewers praised the game for having more intricate, well-paced gameplay than Half-Life 2.[11][28] The game's interactivity, particularly in the form of Alyx and her reactions to the player's actions and the events of the game, was also singled out for praise.[24] PC Gamer commented that "while this inaugural episode may not be the essential FPS that Half-Life 2 is, I can't imagine any shooter fan who'd want to miss it."[25] In its review, PC Gamer UK directed particular praise to the balance between puzzle-oriented and action-oriented challenges throughout the game.[6] In Australia, the magazine PC PowerPlay awarded the game 10 out of 10.[35] Edge praised the "deftness" with which the game was able to direct the player's eyes, and the strength of Alyx as a companion, concluding, "In an interactive genre bound to the traditions of the pop-up gun and invisible hero, it simply doesn't get more sophisticated than this."[26] Episode One earned scores of 87/100 and 85.59% on review aggregators Metacritic[22] and GameRankings respectively.[23] IGN awarded Episode One "Best PC FPS of 2006" and described it as a "great bang for the buck using Valve's new episodic plan", although it did not offer "the complete experience that Half-Life 2 was".[36] GameSpy ranked Episode One ninth on its 2006 "Games of the Year" list, and it also noted the implementation of Alyx as a believable and useful companion.[37]

A common criticism of the game is its short length. Episode One takes roughly 4–6 hours to complete, which raises the issue of whether the game justifies its price.[11] Computer Games Magazine argued the futility of reviewing the game due to its episodic nature; as the first part of a three-part story arc, it is difficult to judge it when divorced from the final product.[38] Game Revolution expressed disappointment at a lack of new features such as environments and weapons.[5]


  1. ^ "The Orange Box for Xbox 360: Release Summary". GameSpot. CNET Networks, Inc. Archived from the original on June 2, 2013. Retrieved 2013-03-16.
  2. ^ "The Orange Box PlayStation 3: Game Editions". IGN. Retrieved 2016-03-30.
  3. ^ "Half-Life 2, Half-Life 2: Episode One and Half-Life 2: Episode Two Updates Released". Steam. Valve Corporation. 2010-05-26. Retrieved 2010-05-26.
  4. ^ "Half-Life 2: Episode One updated". Steam. Valve Corporation. 2013-06-26. Retrieved 2014-01-02.
  5. ^ a b c Colin (2006-06-21). "Episode One review". Game Revolution. Retrieved 2007-04-29.
  6. ^ a b c d "Review: Half-Life 2: Episode One". PC Gamer UK. July 2006.
  7. ^ "Basics (Half-Life 2)". IGN. Retrieved 2008-10-27.
  8. ^ "Basics (Half-Life 2: Episode One)". IGN. Retrieved 2008-10-27.
  9. ^ Lee, Garnett (2005-08-29). "Half-Life 2: Episode One Preview". 1UP.com. Archived from the original on 2011-05-23. Retrieved 2007-10-12.
  10. ^ Berghammer, Billy (2006-05-26). "Half-Life 2: Episode One Hands-On, Details, And Extensive Video Interview". Game Informer. Archived from the original on June 16, 2008. Retrieved 2008-05-12.
  11. ^ a b c d Ocampo, Jason (2006-06-02). "Episode One review". GameSpot. Archived from the original on 2009-09-24. Retrieved 2007-04-28.
  12. ^ a b "Half-Life: The Story so Far". Valve Corporation. Archived from the original on 2008-07-25. Retrieved 2008-03-24.
  13. ^ Bokitch, Chris (2006-05-22). "Valve press release". Steam. Retrieved 2007-04-29.
  14. ^ a b "The Valve team (staff bios)". Valve Corporation. Archived from the original on 2007-04-09. Retrieved 2007-04-29.
  15. ^ Porter, Will (2006-04-13). "Half-Life 2: Episode One Preview". Computer and Video Games. Archived from the original on 2008-05-03. Retrieved 2007-04-29.
  16. ^ a b "Preview: Half-Life 2: Aftermath". PC Gamer UK. May 2005.
  17. ^ "Half-Life 2 Aftermath Q&A". GameSpot. 2005-06-29. Retrieved 2007-05-03.
  18. ^ a b c d e Half-Life 2: Episode One, Chapter V: Exit 17, Developers commentary (DVD). 2006.
  19. ^ a b Bramwell, Tom (2006-06-06). "Opening the Valve". Eurogamer. Retrieved 2007-04-29.
  20. ^ Adams, Dan (2006-04-27). "Half-Life 2: Episode One Interview". IGN. Retrieved 2008-05-12.
  21. ^ Half-Life 2: Episode One—Developers commentary. Valve Corporation. 2006.
  22. ^ a b "Half-Life: Episode One on Metacritic". Metacritic. Retrieved 2012-04-14.
  23. ^ a b "Half-Life: Episode One on GameRankings". GameRankings. Retrieved 2012-04-14.
  24. ^ a b Accardo, Sal (2006-06-01). "Half-Life 2: Episode One review". GameSpy. Retrieved 2007-05-01.
  25. ^ a b "Review: Half-Life 2: Episode One". PC Gamer. August 2006.
  26. ^ a b "Half-Life 2: Episode 1 Review". Edge. 2006-06-08. Retrieved 2012-04-14.
  27. ^ McNamara, Tom (2006-06-01). "Half-Life 2: Episode One". IGN. Retrieved 2008-05-12.
  28. ^ a b Dahlen, Chris (2006-06-13). "Half-Life 2: Episode One". The Onion. Archived from the original on 2008-12-27. Retrieved 2008-10-19.
  29. ^ "Buy Half-Life 2: Episode One". Steam. Retrieved 2008-10-19.
  30. ^ "Half Life 2: Episode One (PC-DVD)". Amazon.com. Retrieved 2007-04-30.
  31. ^ "Half-Life 2: Episode One Pre-Loading Now". Steam. Retrieved 2007-04-29.
  32. ^ Thorsen, Tor (2006-08-24). "Half-Life 2: Episode Two pushed to 2007?". GameSpot. Retrieved 2007-04-30.
  33. ^ Ocampo, Jason. "The Return of Team Fortress 2 and Other Surprises". GameSpot. Retrieved 2007-08-25.
  34. ^ Remo, Chris (2008-12-03). "Analysis: Valve's Lifetime Retail Sales For Half-Life, Counter-Strike Franchises". Gamasutra. Retrieved 2008-12-03.
  35. ^ "Review: Half-Life 2: Episode One". PC PowerPlay. August 2006.
  36. ^ "Best of 2006". IGN. Archived from the original on 2013-10-14. Retrieved 2007-04-28.
  37. ^ "2006 Games of the Year". GameSpy. Archived from the original on 2007-04-29. Retrieved 2007-05-01.
  38. ^ "Half-Life 2: Episode One review". Computer Games Magazine: 57. September 2006.

External linksEdit