An unknown virus spreads across the globe, turning ordinary people into ravenous killers. Only a small population proves to be immune, but most quickly fall prey to the infected. Isolated on the rooftop of a school near the outskirts of Chicago, Bill Thompson and a small band of survivors come to the frightening realization that, without food or water, they will perish quickly under the hot sun. Some wish to migrate to a safer, more plentiful refuge, but the school is surrounded by rampaging murderers. Without a plan, Bill and his group don't stand a chance. Their only hope lies in their one advantage over the infected: their ability to think. Not far away, a leader rises amongst the psychos, a man stricken by the virus yet still intelligent and in control. His need to destroy humankind becomes an obsession, and he rallies an army of killers to seek out and destroy all who remain unchanged. Now Bill and his fellow survivors not only need a safe haven, they must also escape legions of hungry infected. But the virus and its hosts will find them, no matter where they hide, because even sanctuary has its perils.