The United States is devastated by a mysterious phenomenon that reanimates recently-deceased human beings as flesh-eating zombies. Three weeks into the crisis, it has been reported that millions of people have died and reanimated despite the government’s best efforts; social order is collapsing. Rural communities and the National Guard have been effective in fighting the zombie hordes in open country but urban centers are helpless and overrun.
At a television studio in Philadelphia, staff members Stephen Andrews and Francine Parker are planning to steal the station’s traffic helicopter to escape the city. Police SWAT officer Roger DiMarco and his team raid a housing project where the residents are defying the martial law of delivering their dead to National Guardsmen. Some of the armed residents fight back. The raid descends into chaos when Wooley, a brutal and racist trooper, begins firing randomly at the mostly black and Latino residents before being killed himself. Other residents are killed by both the SWAT team and their own reanimated dead. During the raid, Roger meets Peter Washington, part of another SWAT team, and they partner up together. Roger tells Peter that his friend Stephen intends to flee and suggests Peter come with them. They are informed by an elderly priest of a group of zombies in the basement, which they assist in the grim job of destroying.
Later that night, Roger and Peter rendezvous with Francine and Stephen and leave Philadelphia in the helicopter. Following some close calls while stopping for fuel, the group comes across a shopping mall, which they make their sanctuary. They devise an operation to block the mall entrances with trucks to keep the undead from penetrating. Peter and Stephen also cover the access to the stairwell. During the operation, Roger has a near-death experience and becomes reckless as a result. He is soon bitten by the zombies.
After clearing the interior of zombies, the four enjoy a hedonistic lifestyle with all the goods available to them, furnishing their makeshift apartment with the mall’s many commodities. Roger eventually succumbs to his wounds, reanimates and is killed by Peter. After several months, all emergency broadcast transmissions cease, suggesting that the government has collapsed and a large portion of the population has become zombies. Francine, now showing her pregnancy, presses to leave the mall. Supplies are loaded into the helicopter. Stephen also gives Francine flying lessons.
A gang of nomadic motorcyclists, having seen the helicopter, arrives to conquer the mall, destroying the barriers and allowing hundreds of zombies inside. The rioting bikers enrage Stephen and he foolishly starts a gun battle with them. Stephen is soon shot, then bitten by the undead. As some of the bikers are eaten by zombies, the rest retreat with their stolen goods. Now reanimated, Stephen, acting on a remnant of his memories, tears down the wall covering the stairwell and leads the undead to Francine and Peter. Peter kills Stephen while Francine escapes to the roof. Peter locks himself in a room and contemplates suicide but when zombies burst in, he has a change of heart and fights his way up to the roof, where he joins Francine. The two then fly away in the helicopter to an uncertain future.