The world went boom, uleashing a virus which turned the surviving humans into shock-white nocturnal creatures... except for the scientist (Chuck Heston) who discovered an antedote for the cure. So he spends his days rummaging through the city, being careful to avoid any dark places, and shooting anything that moves. At night, he holes himself in his loft, taunted from the "family" of creatures on the streets.
There are other survivors, though, who the scientist eventually meets up with, but it's only a matter of time before they turn to the "other side" too. They figure out how to strain an antedote from the scientist's blood, and do so. Eventually, the creatures catch up with the humans but the hope is still alive.
Starting off with so many possiblilities, the film eventually wallows into a boy meets girl rut, with "romance montages" strewn throughout the middle of the film. A good movie for its time, it could be remade into something wholly better.