Harry is the last line of defense as alien invaders sweep across Earth, converting human beings into mindless zombie slaves. Armed with a powerful flamethrower and weapon dispensers stocked with photon cannons, guided missiles, grenades, and shields, he infiltrates an alien vessel buried beneath a sprawling high-rise metropolis. His ultimate weapon—the Omega bomb—may be the only thing capable of ending the occupation, but getting to it means fighting through wave after wave of mutated former civilians and armored extraterrestrial soldiers.