However, due to the fact that the second half of the game takes place on the unknown planet Pandora, there is not much reference to the Half-Life series at all. The majority of the Half-Life 2 content is based on the storyline of the first game, as most of the main characters appear in all episodes.

There, Freeman fights his way through the facility, while battling against Combine units and battling the evil humans who want to take over the world using advanced technologies. This allows him to travel to another part of the facility, where he meets up with the resistance group known aperture. As the situation worsens, Freeman sends for help but is stopped at a gate guarded by Combine troops. The story of Half-Life 2 follows around two years after the events of the first game, as Freeman becomes trapped inside a Combine stronghold, while the Combine's scientists continue to work on their new project. Freeman is joined by his allies, including a mysterious girl named Alyx, who also survived the Combine attack. It chronicles the origins of the character Gordon Freeman, who must rescue the planet Earth from the evil scientists and agents of the Combine, which want to use the Earth for their own benefit. The first episode in the series, Half-Life 2: Episodes from Liberty City, is not set in the Half-Life universe. Unlike the first Half-Life game, it incorporates more shooting, narrative, and puzzle elements, and adds new features like actual physics and vehicles. Half-Life 2: Episodes from Liberty City is the second installment in the Half-Life series, developed and published by Valve Corporation.

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