Quake II

Humanity is locked in a desperate war against the Strogg, a merciless alien race of cyborgs who convert the living into machines of war. In a bold gambit to end the conflict, Earth launches a full invasion of the enemy homeworld, Stroggos. The assault falls apart on arrival, and a lone marine crash-lands as the only survivor of his squad, stranded deep in hostile territory. Cut off and alone, he must fight through the Strogg's sprawling industrial city, striking at their defenses and war effort to cripple the alien threat.