Half-Life 2: Episode One
=== Setting ===
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.
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.
=== Plot ===
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.
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.
alternate reality, sci-fi