Your unit, Epsilon team, is made up of Black Mesa personnel forced to work for the Administrator's employers (the Organisation). Government forces recently recovered a crystal of immense power - the ownership of which could permanently consolidate the Organisation's hold on Xen. Xen rebels also learnt of this, and planned a major assault on the compound in which it was held.

You were instructed (partly by one of the Administrator's lackeys, the alien clone "Tor") to retrieve the crystal in the resulting confusion. On arrival, though, you found yourself far from the intended insertion point... slap in the middle of the military-rebel conflict.

Worse still, your entire team was led into an aquatic deathtrap. Your lungs strain for air, the floating sensation intensifies, and your vision becomes shaded by ever-darkening void...