Laura Sommers is hearing voices in her head and consults with a psychiatrist. The therapy is suddenly cut short when New York City is rocked by an alien invasion. Laura is knocked out and awakens to an empty, abandoned city. A drifter, Neil, finds Laura and takes her to safety. Hes mentally unbalanced, and ramblingly tries to explain the danger theyre in. He seems to know more than he should about the invasion, but at least he keeps her out of sight of the alien vehicles -- and the attacks of mind-controlled zombies, the remnants of the human population. In a darkened warehouse, a tattered band of survivors struggles to stay undetected. Fighting off the zombies, Laura and Neil join the group, and together, they begin to understand the aliens battle plan. The rest of the citys population has been enslaved. The only ones who have kept their humanity are those with imbalances in brain chemistry -- that is, mental patients. Laura must fight off the zombies to reach the Alpha, the controller, to make the city safe for the survivors. But the voices in her head are growing stronger...