Valve officially announced the development of Half-Life 2: Episode One as the first installment in a series of episodic sequels to Half-Life 2.
The player's arrival in City 17 following the events of Half-Life 2; the Combine still maintain a brutal occupation.
Gordon Freeman and Alyx Vance work together to escape from the Citadel, which is destabilized after the events of Half-Life 2.
The core of the Combine Citadel becomes critically unstable and begins to countdown to a catastrophic explosion.
Gordon and Alyx assist in evacuating civilians from the city before the Citadel's inevitable core explosion.
Intense battles against Combine soldiers and synths as they attempt to slow Freeman and Vance's progress.
Helping Dr. Eli Vance evacuate and ensure safe passage from the Citadel area.
Freeman and Alyx survive the explosion of the Citadel's core, which severely damages City 17.
