Calhoun wakes up at the bottom of the elevator shaft as the only survivor of the crash. After getting up, he finds himself in a storage room, and battles it out with the first ever Xen enemies he's ever seen, such as Houndeyes and Headcrabs. After destroying the generator that was keeping the door for the storage room locked, Calhoun enters a flooded room where a scientist is found hiding in the vents. Surprised to see that Calhoun survived, the scientist informs him that the only way out is to take the path through the Black Mesa Canal, and also asks for Calhoun to not tell anyone that he's down here as the scientist believes that "they" have arrived to kill them all.
Traversing through the facility, Calhoun starts to come across stronger Xen enemies, such as the Vortigaunts, as he enters into the mentioned Canal section of Black Mesa. The Canal turns out to be an industrial waste area where the facility's garbage is destroyed by a river crusher. It soon turns out that the only way forward is to get past the crusher. Traversing the areas surrounding the crusher, Calhoun calls down an elevator that drops a box of explosives into a nearby room. Calhoun then makes his way through a sewer area filled with Zombie Scientists and Bullsquids to reach the room with the explosives. He then proceeds to drop the box of explosives into the river crusher, which causes a big explosion that destroys it. Beyond the crusher, Calhoun climbs his way up to a sewer tunnel where a couple HECU soldiers are seen dropping corpses of the Black Mesa employees down into the Canal to dispose of them; given Calhoun the idea that they're the enemies that the scientist warned him about earlier. Calhoun continues down the tunnel until finding a sewer hatch ladder that takes him out to the surface.
This Chapter contains examples of:
- Alien Invasion: The first level that has Calhoun fighting against the Xen aliens.
- Call-Back: The HECU soldiers at the end of the chapter are heard complaining about how they're stuck cleaning up the mess just because "Shepard's team didn't make it." This is an obvious reference to the beginning of Half-Life: Opposing Force.
- Road Block: Several.
- Escaping the beginning storage room is impossible until the power-lock for the door to the next area is shut off, which Calhoun has to destroy a generator to open it.
- The following flooded room also has a chained fence that can only be bypassed after destroying the explosive barrels behind it from a high vent to open up the fence.
- The main roadblock however is the river crusher within the waste Canal. The path foward is beyond the river crusher, which a box of explosives must be dropped into the crusher to destroy it.
- Sidetrack Bonus: There's a side area near the river crusher that's off the main path. However, exploring it will provide Calhoun an early shotgun. Kind of mirrors how a side area in the original game's "Office Complex" provides Gordon with an early shotgun.
- Unintentionally Unwinnable: In the early spilled acid room, there's a locked gate that has to be blown open by climbing up to a vent in order to shoot at the explosive barrels behind said gate to blow it open. It's pretty much impossible to fail as the storage room right before going up into the vent has two pistol magazines, but if you go about wasting all your pistol ammo before the explosive barrels are destroyed, you end up softlocking yourself.
