Alyx: Holy crap. They must have been terrified of this thing.
Eli: I’m trying to figure whether we oughta be.
Alyx climbs through the remains of the city zoo, fighting antlions in addition to Combine soldiers and headcrabs. She also sees turrets firing on Antlions, but doesn't have to face the turrets herself. Alyx learns via Eli that the Combine didn't create the Vault's superweapon; they found it inside an apartment building in the QZ, and it scared them so much that, rather than enter the building to retrieve it, they lifted the whole building into the air and built the Vault around it. Continuing onward, Alyx finds that the Combine are using the antlions for something, apparently milking them of their acid for use in clearing the Xen infestation. As she leaves the zoo, Eli reveals that the Vault is, in actuality, a prison; built to contain some powerful being who the Combine are fearful of. He and Alyx express doubts as to whether they should continue, but decide that freeing a powerful enemy of the Combine is likely worth the risk.
This Chapter contains examples of:
- O.O.C. Is Serious Business: While decrypting the datapod he stole during his imprisonment, Eli discovers that the Combine treated their discovery with enough alarm that they "grabbed the whole building [it was in] and build [the] Vault around it". Alyx comments that the Combine must be scared of what they found if they went to the trouble of doing this.
- Paper Tiger: A cardboard tiger cutout roars at Alyx because a headcrab zombie is hiding behind it.
