Robert Neville (Charlton Heston) was a scientist working on an experimental vaccine as society disintegrated and out of desperation injected himself. The vaccine was effective but far too late.
Now he lives a solitary hedonistic life, picking over the luxuries left behind in the city.
He is not the only survivor. A tiny number live with the infection, pale sickly people who hide by day and are led by the messianic Matthias (Anthony Zerbe) who wants to destroy all the trappings of the former world. Including Neville.
CW: it's a bit Blaxploitation in parts