Half-Life 2: Episode One (2006)
"Half-Life 2: Episode One" is the sequel for the "Half-Life 2." The story takes 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 as they fight in humanity's continuing struggle against the transhuman race 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 story, Gordon travels with Alyx as they attempt to evacuate the city. As episode one comes to an end, Gordon and Alyx are caught in a major accident, and their fates are revealed in the sequel, Episode Two.
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 junk 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. Afterwards, Alyx and Gordon board a train to escape the Citadel. ...
Did You Know? "Half-Life 2: Episode One" was originally named "Half-Life 2: Aftermath," but was renamed to Episode One after planning to make the game episodic.