This chapter sees Gordon and Alyx fleeing through the city's ruined, dark, and zombie-infested City 17 Underground as they continue to flee the city.
Alyx is trapped under a Combine Prisoner Pod with a restrained Stalker viciously attempting to break loose, relying on Gordon to set her free. After escaping from the train, the duo fights through the rubble of dark, deserted, underground parking garages and tunnels, searching for a way to head up to the surface of the city. In the process, they block off Antlion burrows, and battle various zombies in a pitch-black environment, including zombified Combine soldiers, which were never seen during Half-Life 2. These zombified soldiers, referred to as "Zombines" by Alyx, are a prominent sign that the Combine is losing control of City 17.
This chapter contains examples of:
- Blackout Basement: Many areas in this chapter. It's so dark that Alyx constantly needs Gordon's Ten-Second Flashlight and flares found on the floor to target enemies.
- Drought Level of Doom: This chapter, set mainly in abandoned highway tunnels and parking lots beneath City 17, which have even less in the way of ammo and other supplies than Ravenholm. To make matters worse, the tunnels are swarming with Antlions in addition to hordes of zombies. Be prepared to rely on Alyx to do a lot of the fighting for you.
- Reverse Escort Mission: It's an underground level in which you must spend a part of it pointing a flashlight at enemies for Alyx to shoot them, as there was very little ammunition for you to use at first.
