Deep in the bowels of a decommissioned missile base at Black Mesa, a team of scientists is hard at work on a top-secret government project. You are Gordon Freeman, a young anomalous materials researcher with a limited security clearance and no idea how dangerous your job and world is about to become... until you hear screaming. Next thing you know, hordes of monsters are pouring in through a rift in the fabric of reality as the space-time continuum shatters. And before you can say "anomalous materials," madness rules the world.