A fierce battle is raging between the Race X creatures, the Black Ops contingent(including several snipers) and the remnants of the HECU and the Xen creatures 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. Here, a Gargantua has been trapped on top of the dam and several Marines are attempting to kill it. Shephard uses explosives to destroy the creature and leaves the area through the dam's exposed water pipes.