Earth is under siege by an alien race. The Strogg are cybernetic warriors-a mechanical frame and decaying body parts stabilized by flesh consumed in a systematic annihilation of other species and civilizations. In a desperate attempt to survive a Strogg attack on Earth, an armada of Earth's finest warriors is sent to take the battle to the Strogg home planet. Earth's initial assault force is nearly annihilated immediately, but one marine manages to infiltrate the base, bring down their planetary defense systems, and kill the Strogg's collective brain and leader-the Makron. Earth assumed the destruction of the Makron would end it all, but it didn't.
That's where QUAKE II leaves off and QUAKE 4 begins...
The Strogg are quickly regrouping. However, with the Strogg's planetary defenses still destroyed, Earth's forces can deliver a full and final assault. This time, you're not alone. You are Matthew Kane, an elite member of Rhino Squad, and part of Earth's next invasion wave. An army of soldiers are fighting with you and an arsenal of weapons and vehicles are at your disposal in this heroic and epic battle between worlds.
In Quake IV, you are Matthew Kane, an elite member of Rhino Squad and Earth's valiant invasion force. Fight alone, with your squad, and in hover tanks and mechanized walkers as you engage in a heroic mission into the heart of the Strogg war machine. But, in this epic war between worlds, the only way to defeat the Strogg is to become one of them. Battle through early missions as a deadly marine, then, after your capture, as a marine-turned-Strogg with enhanced abilities and the power to turn the tide of the war.