From his elevated vantage point inside a fortified apartment building, a man watches as madness reigns in the streets below. Something has turned the people of Philadelphia into mindless killers, maniacs whose laughter fill the streets and alleyways. There have been scarce television broadcasts. The radio has offered no new information in days. From all appearances, no help is coming. Just when all seems lost, a military helicopter passes overhead, criss-crossing the city. A loudspeaker attached to the chopper issues a cryptic message: