Shepard exits out of the sewer tunnel into Black Mesa's Sector E Biodome Complex, an area of various biosphere chambers and laboratories where scientists studied Xen creatures and fauna upon massive terrariums. The corporal enters the first biosphere where he faces off on a normal grass area against Race X's large Voltigore creature for the first time. He then fights his way into the second biosphere that looks completely like an area that came from the Xen homeworld; even coming with a Xen healing pool.
Exiting the second biosphere, Shepard enters a lab area where the scientists were studying Race X's powerful Spore Launcher, a biological weapon that fires off powerful spore fruits it uses as ammunition. Shepard obtains one for himself, and moves on to the next area where he starts seeing the glowing sprites again that he saw back on Xen. He follows the sprite to the next lab area where the scientists have been studying the Barnacles. Upon checking a research recording, Shepard sees that the scientists have successfully managed to detach a Barnacle from the ceiling. He obtains the detached Barnacle Grapple in the next room, which can be used as a either a weapon to pull things in and eat them, or he uses it as a grappling hook to pull Shepard towards a location that the Barnacle tongue gets attached to.
Leaving the lab area, Shepard fights his way into the third biosphere, which is a normal looking area that's been taken over by Tentacles. He spots the glowing sprites heading towards an open hole high up the biosphere wall, which Shepard uses his Barnacle Grapple to grab hold of the organic wall matter up there, and pulls himself up to the hole. Departing from the Biodome Complex, the corporal enters a vent that takes him to a room with a radio. Shepard hears on said radio a desperate HECU soldier calling for back-up as his squad appears to be struggling against some "worm creature." The corporal then enters back into the vents to proceed to the next area.
This Chapter contains examples of:
- Grappling-Hook Pistol: The Barnacle Grapple is basically this. Shepard shoots out the Barnacle's tongue, and if it latches onto something organic, it pulls Shepard towards the location.
- Hint System: This chapter makes it a lot more clear that the little white sprites first seen in "We Are Not Alone" act as a bit of a guide to help the player know what direction to go. This continues all the way until the end of the game.
