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Half-Life 2: Episode One

Half-Life 2: Episode One / PC
editor score 8.7
user score 8.7
Release Date



First-Person Shooter






Valve Corporation


Valve Corporation


Inside the Citadel
Inside the Citadel
Half-Life 2: Episode One is the first episodic installment of Valve's Half-Life franchise, and the second release in the Half-Life 2 saga. Players once again fill the shoes of Gordon Freeman, and the action picks up not long after the finale of Half-Life 2. Miraculously plucked from the massive explosion of the Combine Dark Energy Reactor by Vortigaunt allies, Gordon and Alyx Vance are tasked with  temporarily stabilizing the Combine Citadel's unstable energy core before it detonates and escaping from City 17 before The Citadel explodes.



Alyx frozen  in time
Alyx frozen in time
Episode 1 begins immediately after the events of Half-Life 2. After the explosion of the reactor in the Citadel, Gordon Freeman is once again put into stasis by G-Man. Things don't go the G-Man's way after Vortigaunts appear to save Alyx and then take Gordon out of stasis. After regaining consciousness outside the Citadel, Gordon reunites with Alyx and Dog and, after talking to Drs Isaac Kleiner and Eli Vance, must re-enter the Citadel and slow down the explosion of the central core which would be catastrophic.

The unstable Citadel Core
The unstable Citadel Core
Alyx and Gordon go back into the Citadel to stabilize the core and after several fire fights with the remaining Combine soldiers are successful in their cause. While still inside the Citadel, Alyx goes delving through the Combine's computer to uncover more information on their plans. She finds out that the Combine deliberately sped up the core meltdown so they are able to send a message back to Combine homeworld. She also finds a message by Judith Mossman describing a new discovery but is stopped after alerting the attention of Combine Advisors.

Alyx with an information screen featuring Isaac Kleiner behind her
Alyx with an information screen featuring Isaac Kleiner behind her
Using the Citadel train system and having downloaded all the required information, Gordon and Alyx make a hasty escape from the Citadel. Unfortunately the train derails on the way to their destination and and the pair are forced to walk the rest of the journey. Whilst in City 17's underground rail network the duo are faced with many enemies including the Zombine, a cross between the normal headcrab zombies and Combine soldiers. Eventually the pair reach the surface and continue their trek to meet up with Eli and the others. Along the way they see that the screens previously used by Wallace Breen as a means of propaganda have been taken over by Dr Isaac Kleiner, who is now urging all citizens to evacuate the city before the cataclysmic Citadel explosion. Gordon and Alyx meet up with their good friend Barney Calhoun who, along with other survivors, are planning to escape City 17 via train. At this point the pair split up to provide a distraction for the people fleeing.

An advisor flees in a pod from the Citadel
An advisor flees in a pod from the Citadel
After completing their objective Gordon and Alyx hastily make there way to the train station to escape the city. The two meet up with Barney again but must help hold off incoming Combine soldier and a Strider. When everyone else has left board a train themselves and programme it to take them out of the city. Whilst the train carries the duo away, in the background the Citadel can still be seen. The Combines message is sent as the core explodes but before this happens several pods can be seen leaving the structure, these pods are the same as the ones seen before carrying Combine Advisors. As the Citadel explodes the force of the explosion can be seen racing towards Gordon and Alyx, the screen fades to white and the game ends.


Gameplay is nearly identical to Half-life 2, with the addition of some new features; The first feature this game introduces is the HDR graphical technology, which was previously showcased in the tech demo Half-life 2: Lost Coast.

A Zombine
A Zombine
If the player walks from a bright room to a dark one, or vice versa, they are temporarily blinded as their 'eyes' adjust.
The second feature is the focus on physics-based combat. For the first half of the game, players either have no weapon besides the Gravity Gun, or have very little ammo. Thus, use of the Gravity Gun becomes essential. The third feature is the advancement in Alyx's AI. For example, if the player shines their flashlight into Alyx's eyes, she will squint and hold up her arm; in the middle of combat with a zombie, she may kick it's headcrab off, or dodge its attacks.
The third feature is the Zombine, a new enemy. This Combine zombie is much faster than its regular counterpart (though it lacks the frightening alacrity of the fast zombie), and can take much more damage. The greatest danger it poses, however, is its tendency to pull out a live grenade and charge towards the player. The player can counter this strategy by grabbing the grenade with the Gravity Gun.

The fourth, and final feature, is the addition of Antlion burrows. These holes will send out an infinite supply of Antlions unless the player manages to cover it with a physics object, such as a car.


To see a full list of weapons in Half-Life 2: Episode One, go to the Half-Life 2 page.


The first expansion to Half-Life 2 features 5 new levels.
  • Undue Alarm
  • Direct Intervention
  • Lowlife
  • Urban Flight
  • Exit 17


While criticized for its lack of variety and short gameplay, Episode One was met with critical acclaim.