After making his way through warehouses filled with Race X creatures and Black Ops fighting, Adrian Shephard arrives at an old industrial area of Black Mesa where an enormous Gene Worm is attempting to come through a portal from the Race X homeworld.

Shephard uses mounted laser weapons to blind and kill it; in its death throes, an enormous teleportation portal spreads outwards and envelops him.

This chapter details Adrian Shephard’s discovery of the mysterious Black Ops’ plan for Black Mesa.

He finds them in an underground parking garage, activating the thermonuclear warhead from the fourth chapter, apparently with the intent of destroying the facility.

Details the fierce battle raging between the Race X creatures, the Black Ops contingent, including several snipers, and the remnants of the HECU in the last hours of the Black Mesa Incident.

Adrian Shephard makes his way through the underground canals and sewers of Black Mesa, fighting through a Voltigore nest, and arrives at the hydroelectric dam featured in the first game.

The chapter details Adrian Shephard’s battle with the monstrous Pit Worm which is blocking his progress through Waste Processing Area 3.

Working his way through the surrounding area (littered with the corpses of the Marines who sent the distress signal in the previous chapter), Shephard manages to dump toxic waste on the Pit Worm, killing it and allowing him to access the next area.

Adrian Shephard is travelling between various biosphere chambers and laboratories featuring massive terrariums used to house Xen fauna being studied by the scientists deep within the Sector E Biodome Complex.

Eventually he reaches an older industrial area, and picks up a radio transmission from a group of marines fighting some kind of massive creature.

In this chapter, Adrian Shephard finds himself in underwater laboratories where several Ichthyosaurs are being held.

After making his way through the labs and freeing a scientist who provides him with information on the area, Shephard is again forced to teleport to Xen and back again to reach a new part of Black Mesa.