Eastern Europe, The years following the invasion of Earth by the Combine.

Gordon Freeman leads a massive assault on the Nova Prospekt containment and experimentation facility. He has with him no army of human soldiers dedicated to the fall of the “Benefactors,” but a seemingly limitless mass of misdirected antlions who’s only concern is to protect whomever carries the chemical pheromones that their instincts have enslaved them to.

During the attack, Gordon comes to a T junction hallway. One section leads to a flight of stairs and deeper into Nova Prospekt, and the other is closed off by iron gates; a river of antlion drones cascading endlessly through a second junction on the other side. Gordon, not caring what the antlions do on their own as long as they don’t turn on him, takes the open path.

Gordon missed something that not even the vortigaunts were able to report of back to the rebels. He missed a place viewed through propaganda as a “Place of Cleansing.” Through that hallway, sat the Combine’s Alembic Arena. The Alembic Arena was a large domed structure built off of Nova Prospekt that was used as a gladiatorial battleground for prisoners and Combine alike. Executions, military field tests, and gambling (Yes, oddly enough, the Combine do gamble every once in a while) took place in this cave-like sparring ground. Spectator view boxes lined the walls and trash, blood, debris and weapons lay splattered or scattered across the floor. There are large gates used for bringing in beasts and participants, and sniper platforms sit above these in case battles get out of hand.

The torrent of antlions destroyed the Alembic Arena; tearing through the concrete walls and killing all forms of life in the place, be they Combine guards, or prisoners scheduled for forced deathmatch and execution. Now that the war is once again fully raging, the Alembic Arena has become a battleground for a new reason. Teams of humans and Combine fight for control of Nova Prospekt in both the locked down areas and in the arena. Some do it for justice, and others for sadistic enjoyment (the humans who kill humans, and combine who kill combine). Secret passage ways must be discovered, supremacy must be maintained, and above all…

…The arena must be “cleansed” of all life.