Quake 4

Story

During the bloody war between the humans and the nightmarish race of Stroggs, a lone marine has infiltrated the planet and murdered their terrible leader. The humans discover, however, that the Stroggs are not so easily defeated and that their only hope lies with a Marine who is no longer fully human. In a desperate war for Earth's survival against an implacable enemy, the only way to defeat him is to become one of them. Equipped with advanced weapons and vehicles and supported by an elite squad of Marines, you take up the fight in the heart of the Stroggs' home planet and become Earth's only hope for victory.